This paper proposes a markup language based on XML for the domain of scientific theory, called theory markup language (TML). The author argues that this markup language allowing structured representations of theories, has the potential to make the search for and analysis of relevant theory more effective. In the first part of the paper the role of theory and its basic elements are discussed. Then a prototype of a document type definition for TML is presented. Finally issues beyond the technical definition of the markup language are addressed; including issues that are relevant for making a theory repository based on TML documents a useful resource for researchers in MIS and other disciplines.