Creating fictional religions is a foundational practice in fantasy literature and gaming traditions, helping readers and players suspend disbelief by supporting narrative coherence and enhancing the plausibility of invented worlds. Well-developed religious systems have the ability to shape and inform social structures, political, authority, and moral frameworks, adding depth to fictional societies. While often necessary to the work, designing these religions also presents challenges, especially when working within narrative or mechanical restraints. This guide examines the core elements of fictional religions, from the deities themselves to cosmology, clerical hierarchies, and interactions with society, drawing from both historical traditions and speculative fiction. It addresses major religious typologies, the role of semi-divine figures, the function of religion in the fictional world, and how it interacts with magic. The approach is descriptive rather than prescriptive, as the work offers analytical frameworks and illustrative examples intended to aid worldbuilders in the development of religions that are adaptable, purposeful, and integrated into a broader world map.