Expansion books for RPGs. Usually priced between 15 and 20 dollars, with some exceptions for some of the mass-produced books companies like White Wolf favor (so-called splatbooks, or small books of 32 or 64 pages that White Wolf also likes publishing for its Aberrant superhero rpg.

First of the two types of sourcebooks are the expansions to the core rules, such as more toys to play with (whether magic or technological) or more types of characters to play.

Second are the types of books that further describe the setting of the game. These books typically advance the metaplot of the game's setting in some way, provide detailed information on a particular region of the setting, and/or provide detailed information of a particular group or organization within the setting.