This paper contributes to the clarification of a design science epistemology. Itpresents different epistemic types related to three stages of the design science process:1) Evaluative and explanatory background knowledge (pre-design knowledge), 2) prospective knowledge with design hypotheses (in-design knowledge) and 3) prescriptive knowledge with design principles (post-design knowledge). The epistemological inquiry adoptsa pragmatist approach and is pursued through a review of design science literature andinformed by an empirical design case on digital support for social welfare allowances.The clarified design science epistemology shows a diversified epistemological landscapewith several epistemic types: evaluative, critical, appreciative, normative, explanatory,prospective, prescriptive, categorial and attributive knowledge. Ways to express theseepistemic types have been proposed in principal clauses. Ways of grounding have beenclarified for each epistemic type. Proposals are given on how to utilize the design science epistemology in relation to design science process models and publication schemas.