Fire Emblem Gaiden (ファイアーエムブレム外伝, Faiā Emuburemu Gaiden, literally "Fire Emblem Side-Story") is the second installment in the Fire Emblem Tactical role-playing game series developed by Intelligent Systems and published by Nintendo. The game was released on March 14, 1992 in Japan. It is also the second Fire Emblem game to be released exclusively on the Family Computer (Nintendo Entertainment System). It serves as a side story to the original game. Set in the same game world, the events of Fire Emblem Gaiden actually take place on a different continent, and thus have no bearing on the first game's story. However, several characters from the original game, such as the pegasus knight sisters, make an appearance.

While the basic battle engine and formula from the original game are still present in Fire Emblem Gaiden, a number of new gameplay features were added or changed. Certain classes feature branching promotion trees, allowing the player to select a character's promotion class. Only special weapons need be equipped, and neither these nor the unit's default weapons will ever break. Spells are learned through leveling up, and they drain the spellcaster's hit points with each use. The game also features an overworld map that players can travel through between battles and towns that can be freely explored, with more territory becoming available as the game progresses.

Despite the numerous changes to the Fire Emblem formula, most of the later games in the series reverted back to the gameplay of the original Fire Emblem before evolving into new directions. Some of these changes, such as a navigable world map and branching class promotions were later used in Fire Emblem: The Sacred Stones, which received critical praise for its design. However, other elements that Fire Emblem Gaiden introduced have not been reused.