An expansion pack is an addition to an existing game. Expansion packs are most commonly released for Computer Games These add-ons mostly add new game areas and/or an extended storyline to a complete and already released game. The original developer may contract out development of the expansion pack to third-party company, or it may choose to develop the expansion itself (see Hellfire for Diablo and Lords of Destruction for Diablo II).

The price of an expansion pack is usually much less than that of the original game. As additions, most expansion packs require the original game in order to play. If a game has had older expansions, new expansion packs often feature all or some of the game's previous expansions. Games with many expansions sometimes begin selling the original game with the oldest expansions, such as The Sims Mega Deluxe (the original game with The Sims Livin Large, The Sims House Party, and The Sims Hot Date). These collections make the game more accessible to new players, but publishers are careful to not make them compete with their own expansions that are still selling.

Some expansion packs do not require the original game in order to use the new content, as is the case with Blue Shift for Half-Life. This type of expansion pack is often termed a "stand-alone expansion pack".

See also

• List of gaming topics
• Mod (computer gaming)

The Expansion Pak is a RAM add-on cartridge for the Nintendo 64 console.