While GURPS Magic provides an extensive treatment of the the standard GURPS magic system, with each very specific spell treated as a separate skill, GURPS Thaumatology, by Phil Masters, looks at alternative approaches (many of them taken from earlier-edition books and articles by a whole range of writers). In other words, it's the magic supplement that manifests GURPS's generic nature; if a setting has Mutually Exclusive Magic or Unequal Rites, this book provides the tools to tackle the subject, customizing different styles of magic, from the structured to the improvisational, as required. All of which is topped off by some example settings to show how to use such ideas.
Two additional short PDF-only supplements, GURPS Thaumatology: Alchemical Baroque and GURPS Thaumatology: Age of Gold, are actually setting books, describing game worlds in which magic of various kinds is a significant factor.
Enchanting Tropes Invoked in this arcane tone:
- Black Box: In a meta sense. Unlike every other system of magic presented, there's no explanation as to how Path/Book Magic works under the hood, meaning the only way to expand upon what is given is by arbitrarily inventing new rituals.
- Element No. 5: The default magic system incorporates the "classical" four elements (fire, water, earth and air) into its colleges of spells. GURPS Thaumatology, which attempts to make the game's treatment of magic more generic and flexible, notes that some traditions have five elements, either adding something like "void" or "sound" to the standard four, or having a different system, such as the Chinese wood, fire, earth, metal, and water. The book therefore offers ways to fit such elements within a version of the game's standard magic system.
- Language of Magic: Syntactic Magic is an in-depth version of this with several examples provided.
- Magic A Is Magic A: The book exists entirely to handle strange and unusual magic systems.
- Runic Magic:: Thaumatology takes the Nordic "Futhark" runes as a working example of an alphabet that can be used with the generalized rules it provides for "symbol magic".