Each Risk game comes with a number of differently-colored tokens denoting armies (originally, one set each of black, blue, green, pink, red and yellow). In the first editions, the playing pieces were wooden cubes representing one army each and a few rounded triangular prisms representing ten armies each, but in later versions of the game these pieces were molded of plastic to reduce costs. In the 1980s, these were changed to pieces shaped into the Roman numerals I, III, V, and X. The 1993 edition introduced plastic Infantry tokens (representing a single unit), cavalry (representing five units), and artillery (representing ten units). The 40th Anniversary Collector's Edition contained the same troop pieces but made of metal rather than plastic. In the 2005 "bookcase" edition, playing pieces are once again wooden cubes. These token types are purely a convention for ease of representing a specific army size. If a player runs out of army pieces during the game, another color may be used to substitute, or another symbolic token to help keep track of armies. Standard equipment also includes five (originally six) dice in two colors: two white dice for the defender and three red dice for the attacker.

Also included is a total of seventy-two Risk cards. Forty-two of these depict territories, in addition to a symbol of an infantry, cavalry, or artillery piece. One of these cards is awarded to a player at the end of each turn if the player has successfully conquered at least one territory during that turn. No more than one card may be awarded per turn. If a player collects either three cards with the same symbol, or one of each, these cards may be traded in for reinforcements at the beginning of a player's turn. These cards can also be used for game set-up (see below for details). Also included are two wild cards that depict an infantry, cavalry, and artillery piece, as opposed to one of the three and a territory. Because these cards have all three symbols, they can match with any two other cards to form a set. Twenty-eight Mission cards also come with the game to be used in the Secret Mission Risk rule variant.

In the 40th Anniversary Collector's Edition the movement route between the territories of East Africa and Middle East was removed; this was later confirmed to be a manufacturing error, an error repeated in Risk II. Subsequent editions restored the missing route. While the European versions of Risk had included the variation Secret Mission Risk for some time, the U.S. version did not have this added until 1993.

Standard

Each player first counts out a number of infantry for initial deployment. The number of starting armies depends on the number of players. If two are playing, then each player counts out 40 infantry, plus 40 more from a different color set. This third set is neutral and only defends if attacked (the player not attacking rolls for the neutral armies). If three are playing, each player counts out 35 infantry; four players, 30 infantry; five players, 25 infantry; six players, 20 infantry. Players then take turns claiming territories by placing an infantry on an unoccupied territory until all the territories are occupied. Players then take turns placing their remaining armies on their territories. Having done this, the actual game begins with another roll of a die, which is used to determine the playing order.

Alternate

An alternate and quicker method of setup from the original French rules is to deal out the entire deck of Risk cards (minus the wild cards), assigning players to the territories on their cards. As in a standard game, players still count out the same number of starting infantry and take turns placing their armies. The original rules from 1959 state that the entire deck of Risk cards (minus the wild cards) is dealt out, assigning players to the territories on their cards. One and only one army is placed on each territory before the game commences.

There are three main phases to a player's turn: getting and placing new armies, attacking, and fortifying.

Getting and placing new armies

Continent	Bonus Armies
Asia	7
North America	5
Europe	5
Africa	3
Australia	2
South America	2

Players draft new armies and then distribute these pieces to any of their territories at the beginning of their turn. The number of armies a player may draft hinges upon three factors: number of territories owned; continent bonus(es); and redeeming Risk cards. To calculate the number of armies drafted for number of territories owned, players divide their total number of territories by three and round down to the nearest integer. If this result is less than three, round up to three armies. Players also receive bonus armies for occupying an entire continent (see table to the right). Lastly, players may receive armies for turning in a set of three Risk cards. A set may consist of the three different army units (soldier, cavalry, artillery) or be three of a kind (e.g. all three cards have cavalry pictures). If the player has five cards, the player must trade in a set. The first set to be turned is worth 4 reinforcements; the second is worth 6; third, 8; fourth, 10; fifth, 12; sixth, 15 and for every additional set thereafter 5 more armies than the previous set turned in; the number of reinforcements received is shown by a Golden Cavalry which moves along a grid every time a set is traded in. The probability of having a tradeable set of cards, holding three cards is 33.3% (9/27), holding four cards is 74% (60/81), and 100% holding 5 cards (243/243).

The player places these armies on any of his territories. If a player owns one or more of the territories depicted on the set of turned in cards, the player may choose one of these territories to be awarded two additional armies that must be placed in that territory.

Attacking

When it's a player's turn to attack, he or she can only attack territories that are adjacent or connected by a sea-lane to his or her own territory. A battle's outcome is decided by rolling dice. The attacking player attacks with one, two, or three armies, rolling a corresponding one, two or three dice. At least one army must remain behind in the attacking territory not involved in the attack, as a territory may never be left unoccupied. Before the attacker rolls, the defender must resist the attack with either one or two armies (using at most the number of armies currently occupying the defended territory) by rolling one or two dice. Each player's highest die is compared, as is their second-highest die (if both players roll more than one). In each comparison, the highest number wins. The defender wins in the event of a tie. With each dice comparison, the loser removes one army from his territory from the game board. Any extra dice are disregarded and do not affect the results.

If an attack successfully eliminates the final defending army within a territory, the attacker then must occupy the newly conquered territory with at least the number of attacking armies used in the last round of attack. There is no limit to the total number of additional armies that may be sent in to occupy, providing at least one army remains behind in the original attacking territory. Players may attack any number of territories any number of times before yielding the turn to the next player. Attacking is optional; a player may decline to attack at all during the turn.

If an attacker occupies a defender's last territory, the defender is eliminated from the game and the attacker acquires all of the defender's Risk cards. If the conquering player then holds five or more cards, the player must trade in sets until the player has fewer than five. The gained armies are placed immediately.

If, at the end of attacking, at least one territory was conquered that turn, the player draws a Risk card from the deck.

Fortifying

When finished attacking and before passing the turn over to the next player, a player has the option to maneuver any number of armies from a single territory occupied by the player into an adjacent territory occupied by the same player. This is sometimes referred to as a "free move". Under an alternate rule, the maneuvering armies may travel through as many territories to their final destination as desired, providing that all involved pass-through territories are connected and occupied by that same player. As always, at least one army must be left in the originating territory. However, the player can only distribute between two territories. Play then proceeds clockwise to the next player.

Basic strategy

The official rulebook gives three basic strategy tips for the classic rules:

• First, players should control entire continents to get the bonus reinforcement armies.
• Second, players should watch their borders for buildups of armies that could imply an upcoming attack.
• Third, players should build up armies on their own borders for better defense.

Holding continents is the most common way to increase reinforcements. Players often attempt to gain control of Australia early in the game, since Australia is the only continent that can be successfully defended by heavily fortifying one country (either Siam or Indonesia). Generally, continents with fewer borders are easier to defend as they possess fewer points that can be attacked by other players. South America has 2 access points, North America and Africa each have 3, Europe has 4, and Asia has 5.

Generally, it is thought advisable to hold Risk cards until they can be turned in for maximum reinforcements. This is especially true earlier on in gameplay, because extra armies make a greater difference in the beginning of the game. Eliminating a weak player who holds a large number of Risk cards is also a good strategy, since players who eliminate their opponents get possession of their opponents' Risk cards. In this case, trading in Risk cards earlier may help acquire the necessary troops. If the conquering player has five or more Risk cards after taking the cards of another player, the cards must be immediately turned in for reinforcements until the player has fewer than five cards and then may continue attacking.

"Turtling" is a defensive strategy where a player who feels vulnerable tries to become too expensive to be removed while remaining a threat to harass other players. The objective of this strategy is to not be defeated. A player using this strategy might remain in the game all the way to later stages and then mount an attack on the weakest player and start a chain elimination to remove one player after another to win the game. The player who uses this strategy is called a Turtle. The term was popularised in Real-time Strategy games where a player creates a defensive perimeter or a “Turtle Shell” around the base of operations. Solutions to counteract this strategy using cooperation have been proposed by Ehsan Honary.

Alliances

The rules of Risk do not endorse or prohibit alliances or truces. Thus players often form unofficial treaties for various reasons, such as safeguarding themselves from attacks on one border while they concentrate their forces elsewhere, or eliminating a player who has grown too strong. Because these agreements are not enforceable by the rules, these agreements are often broken. Alliance making/breaking can be one of the most important elements of the game, and it adds human interaction to a decidedly probabilistic game. Some players allow trading of Risk cards, but only during their turn. This optional rule makes alliances more powerful.

Dice probabilities

Defenders always win ties when dice are rolled. This gives the defending player the advantage in "one-on-one" fights, but the attacker's ability to use more dice offsets this advantage, as indicated in the dice probability charts below. Actually capturing a territory depends on the number of attacking and defending armies and the associated probabilities can be expressed analytically using Markov chains, or studied numerically using stochastic simulation.

It is always advantageous to roll the maximum number of dice, unless an attacker wishes to avoid moving men into a 'dead-end' territory, in which case he may choose to roll fewer than three.

The table below states the probabilities of all possible outcomes of one attacker dice roll and one defender dice roll.  Green  indicates an advantage to the attacker and  red  an advantage to the defender.

Outcome probabilities of one dice roll in Risk (various number of die)			Attacker
			one die	two dice	three dice
Defender	one die	Defender loses one	41.67%	57.87%	65.97%
		Attacker loses one	58.33%	42.13%	34.03%
	two dice	Defender loses one	25.46%	N/A	N/A
		Attacker loses one	74.54%	N/A	N/A
		Defender loses two	N/A	22.76%	37.17%
		Attacker loses two	N/A	44.83%	29.26%
		Each loses one	N/A	32.41%	33.58%

Thus when rolling three dice against two dice (the most each player can roll), three against one, or two against one, the attacker has a slight advantage, otherwise the defender has an advantage. When large armies face off, a player will tend to gain a greater advantage over his opponent by attacking rather than defending. (Multiple opponents can change the prudence of such a strategy, however.)

The following table shows the probabilities that the attacker wins a whole battle between two countries (a sequence of dice rolls).  Green  indicates an advantage to the attacker (i.e. that the probability to win is larger than 50%), and  red  an advantage to the defender.

Probabilities of attacker winning a whole battle in Risk		Number of attacking armies
		1	2	3	4	5	6	7	8	9	10
Number of defending armies	1	42%	75%	92%	97%	99%	>99%	>99%	>99%	>99%	>99%
	2	11%	36%	66%	79%	89%	93%	97%	98%	99%	99%
	3	3%	21%	47%	64%	77%	86%	91%	95%	97%	98%
	4	1%	9%	31%	48%	64%	74%	83%	89%	93%	95%
	5	<1%	5%	21%	36%	51%	64%	74%	82%	87%	92%
	6	<1%	2%	13%	25%	40%	52%	64%	73%	81%	86%
	7	<1%	1%	8%	18%	30%	42%	54%	64%	73%	80%
	8	<1%	<1%	5%	12%	22%	33%	45%	55%	65%	72%
	9	<1%	<1%	3%	9%	16%	26%	36%	46%	56%	65%
	10	<1%	<1%	2%	6%	12%	19%	29%	38%	48%	57%

The number of attacking armies does not include the minimum one army that must be left behind in the territory (e.g. if the attacking territory has 10 armies total, it has maximum 9 attacking armies).

A common situation is that the attacker wants to take over a whole region of countries during the same round, by a series of battles. After each successful battle, the attacker leaves one army in that country, and continues with the remaining attacking armies into next country. The following table shows the average number of countries that the attacker can take over, as well as the 90 percentile, starting with a certain number of attacking armies in the first battle. A fixed number of armies is assumed to defend each country.

	Number of attacking armies in the first battle:	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
One defending army in each country	Average number of countries that can be defeated:	0.42	1.0	1.7	2.3	3.0	3.6	4.3	5.0	5.6	6.3	6.9	7.6	8.3	8.9	9.6	10.2	10.9	11.5	12.2	12.9
	Number of countries that can be defeated with 90% confidence:	0	0	1	1	2	2	3	3	4	4	5	5	6	7	7	8	8	9	10	10
Two defending armies in each country	Average number of countries that can be defeated:	0.11	0.39	0.82	1.2	1.6	2.0	2.4	2.8	3.2	3.6	3.9	4.3	4.7	5.1	5.5	5.9	6.3	6.7	7.1	7.5
	Number of countries that can be defeated with 90% confidence:	0	0	0	0	0	1	1	1	2	2	2	2	3	3	3	4	4	4	5	5

Over the years, Parker Brothers and Hasbro have published many different editions of rules for the game.

Two-player Risk

This 2-player version is played according to the traditional rules of Risk. Each player takes 40 armies and alternately places one army on an unoccupied territory until each has occupied 14 territories. The remaining armies are alternately distributed on the occupied territories. The remaining 14 territories are occupied by a force called the Allied Army. These armies are composed of playing pieces different in color from those used by the two players. Two Allied Armies will be placed on each unoccupied territory for a total of 28 armies.

Each player attacks according to the traditional rules. A player may attack the other player or the Allied Army. When a player attacks the Allied Army, the other player rolls the dice for the Allied Army.

The game ends when one player loses all his territories. If the Allied Army loses all its territories, game play is continued according to the traditional rules.

Capitol Risk

Each player has a "capitol" in one of the initially-occupied territories. The player to capture all capitols wins. Any armies and territories that belong to the losing nation are turned over to the victor. Capitol Risk often leads to much shorter games.

Secret Mission

Secret Mission Risk was the standard game in European editions for some decades and was introduced to US editions in 1993. This form of play gives each player a specific mission short of complete world domination. Players do not reveal their missions to each other until the end of the game. The game ends when the first person to complete his mission reveals his Secret Mission card, thereby winning. In 2003, a different Secret Mission version of the game was released, in which each player received four (easier) secret missions to complete.

The original missions in the 1993 US edition are:

• capture Europe, Australia and one other continent
• capture Europe, South America and one other continent
• capture North America and Africa
• capture North America and Australia
• capture Asia and South America
• capture Asia and Africa
• capture 24 territories
• capture 18 territories and occupy each with two troops
• destroy all armies of a specific color or—if one's own troops are that color—capture 24 territories (one mission for each color)

Note: In the UK edition, if a player's mission is to destroy all armies of a particular color, and another player kills off the last armies of that color, their mission changes to capturing 24 territories. In the US edition, no matter who eliminates the last army, the player with the mission wins automatically

Alternate card turn-in rules

In some editions, the cards display either one or two stars. Cards may be exchanged to draft a number of armies depending on the sum of these stars (limited from 2 to 10 stars) according to the table below. Cards may be accumulated as long as the player wishes. The new armies are immediately deployed in any combination across the player's occupied territories.

Number of Stars exchanged	Number of Troops received
2	2
3	4
4	7
5	10
6	13
7	17
8	21
9	25
10	30

If an Objective has been accomplished on the player's turn, that player is prohibited from also drawing a Risk card on that turn. The territory on the card is irrelevant when drafting troops.

An additional card exchange regime is to offer a fixed number of armies depending on the emblem on the card. Three infantry would receive four armies, three cavalry would receive six armies, three cannons would receive eight armies, and one of each emblem would receive 10 armies.

Yet another card exchange regime follows the escalating exchange rules, but after awarding 15 armies for the sixth exchanged set the number is reset to the original four armies before increasing again with each exchange.

Other rule variations

The official rulebook suggests variations to the game-play mechanics for "Risk experts," any or all of which can be used depending on player preference. These suggestions include:

• Reducing the rate at which Risk card sets increase in value so that they only go up by 1 each time
• Allowing for armies to move to any controlled territory if it has contiguity between it and its destination. (Rather than only an immediate neighbor)
• Granting an attack advantage (the option to re-roll one die per battle) when attacking from or to a territory for which the attacker holds a Risk card.
• Granting attackers the ability to change one of the dice rolled so that a six is showing. An attacker may do this only once per turn.

In addition to these official variations, many computer and Internet versions have different rules, and gaming clubs often use house rules or competition-adjusted rules. These may include structure such as forts, freeplay (players take turns simultaneously), or other rules.

There have been other variations of Risk, essentially "house rules," complete with titles like "Ultimate Risk" (which is played in the United States).

The following is a typical layout of the Risk game board, with a table of the corresponding continent and territory names. Each territory on the typical Risk game board represents a real-life geographical or political region on Earth. As such, the territory borders are drawn to resemble the geography of those regions. This provides an interior space on which to place the army units, adds an element of realism to the game, and also adds complexity.

The numbers in parentheses represent the number of additional armies granted during the reinforcement stage of a player's turn who controls all of the territories in that continent.

Note

1. ^ On some versions of the board, Alberta, Ontario, Quebec, Great Britain, Ukraine, Congo, India, and Siam are known as Western Canada, Central Canada, Eastern Canada, Great Britain & Ireland, Eastern Europe, Central Africa, Hindustan, Pakistan, and Southeast Asia, respectively. Not all variations occur concurrently.
2. ^ Note that the territory of Afghanistan does not include the real life country of Afghanistan.

In addition to the original version of 1959, and a 40th Anniversary Edition with metal pieces, a number of official variants of Risk have been released over the years. In recent years, Hasbro has predominantly based its Risk variants on popular films. The most recent example in this trend is the Transformers version, released in June 2007. In chronological order, the variations of Risk that have been released are:

• Castle Risk (1986) – A version focusing only on Europe in which each player has a castle, and the player's goal is to protect the castle from attack. Castle Risk was the first version of Risk released after 27 years of production to depart from standard play. Although it was unsuccessful, it introduced many concepts integrated into later versions of Risk.
• Risk: Édition Napoléon (1999) – Adds generals, fortresses, and naval units.
  • Risk: Édition Napoléon: Extension Empire Ottoman (2000) – Adds a sixth player to Risk: Édition Napoléon.
• Risk: 2210 A.D. (2001) – An award winning futuristic version, produced by Avalon Hill, another division of Hasbro. The game features moon territories, ocean territories and commander units and offers a number of official and unofficial expansions.
• Risk: the Lord of the Rings (2002) – 2–4 player version based on northern Middle-earth.
  • Risk: the Lord of the Rings: Gondor & Mordor Expansion Set (2003) – Extension to Risk: the Lord of the Rings, also includes a 2-player Siege of Minas Tirith mini-game.
• Risk: the Lord of the Rings: Trilogy Edition (2003) – Combines the first two Lord of the Rings versions, but does not include the Siege of Minas Tirith mini-game.
• Risk Godstorm (2004) – A version based on the mythological pantheons of various ancient civilizations; produced by Avalon Hill.
• Risk: Star Wars: Clone Wars Edition (2005) – Set in the Star Wars universe during the Clone Wars. The player can fight on the side of the Separatists or the Republic, using either the classic Risk rules or the Clone Wars variations where altruism pays off.
• Risk Express (2006) - Designed by Reiner Knizia as part of Hasbro's Express line of games (although not as part of the US-released series). Roll different combinations of infantry, cavalry, artillery & generals to capture the territory cards.
• Risk: Star Wars Original Trilogy Edition (2006) – Set during the Galactic Civil War, players play as the Galactic Empire, the Rebel Alliance, or the Hutts. This version is unique in that each of the factions has a different set of goals and victory conditions.
• Risk Junior: Narnia (2006) – Based on The Lion, the Witch and the Wardrobe, players can play as either the forces of Aslan or as the forces of the White Witch.
• Risk: The Transformers Edition (2007) – Based on the Transformers film, players can either play on the side of the Autobots or the Decepticons on a Cybertron stylised map.
• Risk: Black OPS (2008) – Limited edition released in early 2008. Print run was limited to a 1000 copies. Most of the copies were given to people in the board game industry to test out new rules for up coming editions.
• Risk: Balance of Power (2008) - Based on a European map.
• Risk: Reinvention (2009) – Also called Risk Factor or Risk Revised Edition. This is the commercial released version of Black Ops. It features capitals, cities, missions, and very thin pieces shaped like arrows. It is also available with different components (wooden map, wooden cube pieces, etc.) as Risk Onyx Edition.
• Risk: Halo Wars Collector's Edition (2009) – Includes UNSC, Covenant, and The Flood. It has 42 territories and 6 sectors. It was released in Autumn 2009.
• Risk 1959 (2009) – Winning Moves Games USA released a reproduction of the original game of Risk from 1959. It includes all the original graphics, wood pieces, and individual plastic storage boxes.
• Risk: Factions (2010) - a licensed video game version of the game developed by Electronic Arts, and distributed on Xbox Live Arcade and PlayStation Network. Includes a "classic" mode which allows games played using standard original rules, and a "Factions" variation on the rules.
• Risk: Metal Gear Solid (2011) - Announced at San Diego Comic-Con 2011, the game features the five PMCs included in Metal Gear Solid 4: Guns of the Patriots, and gives the opportunity for nuclear strike capabilities if the player controls Metal Gear REX..
• Risk Legacy (2011/12) - A game that has permanent changes to the game board and cards each time you play.
• Risk Halo Legendary (2012)
• Starcraft Risk (2012)- Four play modes with three different races. Each race has two unique hero units.
• Risk: Star Wars Saga Edition (2013)- Announced at UK Toy Fair
• Risk: Mass Effect Galaxy at War Edition (2013) - Announced on February 11th, 2013

Many variants exist that are based on the original concept of the game of Risk and that contain much of the functionality of the original, but are not licensed by Hasbro, such as, for example, the video games Global Domination and Lux. Known as Risk clones, such variants have names not containing the term "Risk" to avoid legal issues. Some of these clones are available commercially, of which many have been released through the iTunes App Store, especially for the iPad. Several other Risk clones are distributed freely over the Internet, such as Dice Wars. Games such as Nintendo Wars can be seen as a complex evolution which still holds some elements from Risk.

In addition to Risk clones, third-party products have been created which slightly modify traditional gameplay. Among the most popular third-party editions are virtual dice-rolling simulators. These can act as virtual replacements to traditional dice or be used to automatically simulate the results of large battles between territories—-significantly speeding up gameplay during battles between territories with many units.

'Anti'-Risk

A number of games aim at peace and disarming instead of world domination. For example, in Glasnost The Game, the winner is the player who manages to achieve complete disarming of all his or her territories. The goal can be achieved only after the player succeeds in conquering almost all territories.

Several computer and video game versions of Risk have been released as The Computer Edition of Risk: The World Conquest Game, starting with the Commodore 64 edition in 1988 and the Macintosh edition in 1989. Since then, various other editions have been released for PC, Amiga, Sega Genesis, PlayStation, PlayStation 2, and Game Boy Advance. In 1996 Hasbro Interactive released a PC version of Risk that included a new variation on the game called "Ultimate Risk", which did not use dice but rather implemented the use of forts, generals, and complex battle strategies. Risk II for PC and Mac was released as a 2000 video game which includes classic Risk as well as board and gameplay variations. In 2010, Pogo.com added a licensed version of Risk to its library of online games. An Xbox Live Arcade version of Risk called Risk: Factions was released on June 23, 2010. It includes classic Risk as well as a factions mode where players can play as Zombies, Robots, Cats, Soldiers, or Yetis.

An official licensed iOS app, "RISK : The Official Game", developed for the iPhone, iPod Touch, and iPad by Electronic Arts, was released on July 16, 2010. Although the iPad version (Risk HD) has to be bought separately from the iPhone version (Risk), local link up allows games to take place across versions. A maximum of 6 players can participate. If only one iOS device is available, the 'pass and play' mode allows several players to take part in a multi-player game.

A version for the Atari 8-bit computers was in development in 1983, to be published by Parker Brothers. An unfinished prototype exists in possession of its programmer Steve Kranish.