A rules heavy game is one that relies strongly upon complex devices, such as cards, dice, tables and mathemtical calculations, to determine the outcomes of actions in the game. For instance such a system might have tables for determining how much damage a character might take from falling a certain height.

There are two main reasons for playing such a system:

1. Some people believe that it is important to simulate reality as closly as possible. Thus they use extensive rules to ensure that the actions of the game are both plausible and consistent.
2. Other players simply enjoy the creation of complex rule systems for its own sake, as an activity quite separate from that of using those rules to play a game. Thus a player might devise a mechanic for representing drinking contests in a specific system, because he had a nice idea of how it might be done.

Compare Systemless Games.