"Witch Hunter: The Invisible World" is a historical fantasy campaign setting with elements of classical horror; it is produced by Paradigm Concepts which also has the d20 Arcanis setting and its associated "living" campaign to its credit. The setting takes place on an alternate Earth in 1698, a world where Hernando Cortez's Spanish expeditionary force was brutally slaughtered by the Aztecs, the Renaissance was muted, the Enlightment never happened, and women have near equity in society.

The system used is proprietary, and exclusively uses d10s in a success-based and contesting fashion that focuses on cinematic rather than "crunchy". Advancement is done through skill points, through which talents (an analogue to feats) and skills (similar to d20 skill ranks), as well as points for the nine core ability scores, can be purchased.