Commander Keen in Keen Dreams is a side-scrolling platform video game developed by id Software and published by Softdisk in 1991 for DOS. It is the fourth episode of the Commander Keen series. The game follows the titular Commander Keen, an eight-year-old child genius, in an adventure in his dreams as he journeys through a vegetable kingdom to defeat the evil potato king Boobus Tuber and free enslaved children from the Dream machine. The game features Keen running and jumping through various levels while opposed by various vegetable enemies; unlike the prior three episodes, Keen does not use a pogo stick to jump higher, and throws flower power pellets to temporarily turn enemies into flowers rather than shooting a raygun to kill them.

After the success of Commander Keen in Invasion of the Vorticons, the developers of the game, including programmers John Carmack and John Romero, designer Tom Hall, and artist Adrian Carmack, left their jobs at Softdisk to found id Software. As part of a settlement for using company resources to make their own game, the group agreed to make several games for Softdisk's Gamer's Edge subscription service. As a part of fulfilling this obligation, id made Keen Dreams as a prototype to develop ideas for their next major Keen game, Commander Keen in Goodbye, Galaxy. These ideas included gameplay changes, graphical enhancements, and artistic improvements. Keen Dreams was not as widely played or noted as the other Keen games, and as it was owned by Softdisk was included in only one of the several compilation releases of the series by id or regular publisher Apogee Software; as a result, it became known as the "lost episode" of the series. In 2013 a port was developed by Super Fighter Team for Android devices.

A 2014 Indiegogo crowdfunding campaign led to the original source code being published and a release by Hard Disk Publishing through Steam for Microsoft Windows and Linux in 2015, and OS X in 2016. A Nintendo Switch version by Lone Wolf Technology was released in 2019. An expanded version was released in 2020 for the Nintendo Switch and Wii U by Diplodocus Games and in 2021 for Windows by the Keen Company under the title "Commander Keen in Keen Dreams: Definitive Edition", featuring additional levels and new music.

Gameplay image from the game, showing Commander Keen and a potato "Tater Trooper" enemy. To the left of Keen are two flower power pellets, while the box in the upper left shows the player's score, lives, and flower power ammo.

Commander Keen in Keen Dreams is a side-scrolling platform video game: the majority of the game features the player-controlled Commander Keen viewed from the side while moving on a two-dimensional plane. The player character can move left and right and can jump; unlike the prior trilogy of episodes in the series, known collectively as Commander Keen in Invasion of the Vorticons, Keen cannot jump higher using a pogo stick. The levels are composed of platforms on which Keen can stand, viewed from slightly above so as to give a pseudo-3D effect, and some platforms allow Keen to jump up through them from below, while others feature fireman's poles that Keen can climb up or down. Once entered, the only way to exit a level is to reach the end, though unlike in Vorticons the player can save their game at any point. In between levels the player travels on a two-dimensional map, viewed from above; from the map the player can enter levels by approaching the entrance or save their progress in the game. Some levels are optional to enter and may be bypassed.

Levels include a variety of anthropomorphic vegetable enemies, such as potatoes and squash, each with different movement patterns and attacks. Levels can also include hazards, such as water or spikes; touching a hazard or most enemies causes Keen to lose a life, and the game is ended if all of Keen's lives are lost. Unlike the previous game, Keen can not shoot enemies with a raygun; instead he collects small pellets throughout the levels called flower power to throw at enemies. If an enemy is hit, they transform into a passive, intangible flower for a limited time, while pellets that do not hit an enemy can be retrieved by the player. The player can also find food items in the form of sweets throughout the levels which grant points, with an extra life awarded if the player earns enough points, as well as figures of Keen that grant an extra life. Placed throughout the levels are collectible bombs, which the player must use at least twelve of in order to defeat the final boss of the game.