Little Big Adventure is a 1994 action-adventure game developed by Adeline Software International. It was published in Europe by Electronic Arts, and by Activision in North America, Asia and Oceania under the name Relentless: Twinsen's Adventure. Over 500,000 copies were sold by 1999. The game was initially released on CD-ROM and some time later on floppy disks; the CD-ROM version features full-motion video, music and speech whereas the floppy disk version has MIDI music files and still images to replace the videos. The game was later ported to the PC-98 and FM Towns and was released in Japan in 1995. It was released for the PlayStation in Japan and Europe in 1996 and 1997 respectively, and to Android and iOS devices in 2014.

In 1997, a PC-only sequel was released under the name of Little Big Adventure 2 (also known as Twinsen's Odyssey).

On October 20, 2015, an "Enhanced Edition" developed by DotEmu was released on Steam, alongside a re-release of the original game. In October 2021 both Little Big Adventure 1 and 2 engines source code were released under the GPL.

Little Big Adventure is a real-time pseudo-3D isometric action-adventure game. All characters and vehicles in the game, including some props in the world, are real 3D polygon-based objects, performing actions within 2D pre-rendered environments. After completion of certain tasks the player is presented with a full-motion video cut-scene. The player-character, Twinsen, can be switched between four different "behaviour modes" (Normal, Athletic/Sporty, Aggressive, and Discreet), each changing the character's abilities and interactions with the game world. Combat in the game is mainly conducted using the Magic Ball, a glowing ball of energy which the player throws towards enemies, the trajectory and angle of the ball changing depending on the mode the player is in. Switching to the "Aggressive" mode also allows Twinsen to engage in combat via punching and kicking.

The gameplay is partially free-roaming, allowing the player free non-linear travel around the islands of the game's world once they have been unlocked by completing certain objectives or solving certain puzzles; there are also many tasks which are optional or non-linear. Certain locations in the game are initially blocked from the player until they progress to a certain stage, such as the islands in the Northern Hemisphere and fortresses on several of the islands in the Southern Hemisphere.

The game features an autosave mechanic, which was a departure from the usual manual save system seen in most games of that time.