Interactive fiction shares much in common with Multi-User Dungeons ('MUDs'). MUDs, which became popular in the mid-1980s, rely on a textual exchange and accept similar commands from players as do works of IF; however, since interactive fiction is single player, and MUDs, by definition, have multiple players, they differ enormously in gameplay styles. MUDs often focus gameplay on activities that involve communities of players, simulated political systems, in-game trading, and other gameplay mechanics that are not possible in a single player environment.