In Fantasy Grounds II modules are packages of content specific to a certain ruleset (this is not strict in the sense that any ruleset can be defined to "accept" data from modules created for some other ruleset). Modules can add camapign data in the various sheets defined in the ruleset. To exemplify, in the d20 ruleset such data can be story book pages, images, personalities that include NPCs and customized monsters, items, tokens or digital miniatures/counters. Modules can additionally create library items such as source books, tables, setting data, etc. Basically, modules are what they are in print media, adventures, settings, compendiums, ...

Modules are activated from a module activation window, if such is included in the ruleset. The Gamemaster can control what modules the players can use; he gets messages whenever a player attempts to open a module book, he can use the module activation window to either allow or block the use of the module. The Gamemaster can additionally force the players to use certain modules (place the corrsponding books in the players' library, e.g.).

Modules can be divided into host data, shared data, and owner data. Host data is always only usable by the Gamemaster. If a player has opened a module with host data, those entries do not show up for her. Shared data is usable by both the Gamemaster and players. If the players do not own the module, the host will send an encrypted version of the shared module data that the players can access while playing in the particular campaign. Owner data is usable only by the player (or Gamemaster) who has the module. The Gamemaster can still disallow the player from opening the module in his campaign. Technically, the different types of data are stored in different XML files included in the Fantasy Grounds .mod-file.