Research and Development is a free mod for the first-person shooter video game Half-Life 2: Episode Two. Developed by Matt Bortolino and released on July 17, 2009,^[1] it is a non-violent first-person puzzle video game, and has been compared to Portal. It received critical praise for its unique gameplay and high development quality.

The game does not have an overt story; the player wakes up as an unnamed character in a detailed but generic location, not knowing how they got there, and must start solving puzzles in order to escape.^[2][3]

The mod takes place in the Half-Life universe, but strips the player of their weapons, giving them only a Gravity Gun and antlion bait.^[3] The player must solve puzzles to traverse the levels, to the point where the game resembles a point-and-click adventure.^[4]

Research and Development utilizes similar puzzles as those seen in between the shooter gameplay in Half-Life 2, but turns them into an entire game.^[4]

Alec Meer of Rock, Paper, Shotgun called the game "as must-play as an [Half-Life 2] mod gets", and stated that the game's non-combative player character is "in many ways more keeping with the mind-over-matter character we're often told Gordon Freeman is than the openly, incongruously murderous role he dons in Valve's games".^[4] Nick Breckon of Shacknews recommended the game, praising its "refreshing amount of original mechanics and crafted special effects".^[2] Tom Sykes of PC Gamer called the game one of the best Half-Life 2 single-player mods, saying that it is "surprising just how easily Half-Life 2's toolset translates" to the new focus of puzzles.^[5] Gry Online called the game's puzzles "ingenious", remarking that their solutions were completely logical.^[6] Anthony Burch of Destructoid stated that the game "provides clever fun in a way very few games - never mind how many modifications - are capable of," and that he "almost [felt] guilty playing this game for free," criticizing some bugs in the game, but calling its final levels "spectacular".^[7]