What kind of knowledge is needed by information specialists working in a specific subject field like medicine, sociology or music? What approaches have been used in information science to produce kinds of domain-specific knowledge? This article presents 11 approaches to domain analysis. Together these approaches make a unique competence for information specialists. The approaches are: producing literature guides and subject gateways; producing special classifications and thesauri; research on indexing and retrieving specialities; empirical user studies; bibliometrical studies; historical studies; document and genre studies; epistemological and critical studies; terminological studies, LSP (languages for special purposes), discourse studies; studies of structures and institutions in scientific communication; and domain analysis in professional cognition and artificial intelligence. Specific examples and selective reviews of literature are provided, and the strengths and drawbacks of each of these approaches are discussed.