To create transparency on the rising plethora of Shadow IT (SIT) and Business-managed IT (BMIT) research, this paper reviews how existing research in the field uses reference theories. A review of 107 SIT and BMIT literature items shows that 52 (49%) of the literature items drew on 37 reference theories for theory testing and theory building. The remaining 55 (51%) literature items did not base their research on reference theories. To guide theorizing in future SIT and BMIT research, this paper argues in favor of "category-spanning" reference theories, i.e., reference theories already used across the SIT and BMIT research categories "causing factors," "outcomes," and "governance of SIT and BMIT." The paper identifies four category-spanning theories: (1) transaction cost theory, (2) agency theory, (3) loose coupling theory, and (4) technological frames. Analyzing the prior use of these reference theories in SIT and BMIT, the paper at hand suggests and discusses extensions for their application in future SIT and BMIT research. In addition to the category-spanning reference theories, the theory of workarounds seems to be highly applicable. Due to the novelty of the research field and the explorative character of most existing studies, the paper calls for enhanced theorizing in the field of SIT and BMIT since currently most of the literature items do not build on reference theories.