When new information technologies emerge, they stimulate the curiosity of Information System (IS) research and practice. Research and practices regarding emerging technologies can be characterized as IS fashions, which can lead to IS innovations. Yet, researchers and practitioners often wonder if these fashions are the next big thing or just a passing fad. One way to determine the contribution of a scientific fashion is to understand its theoretical state and maturity as reported in the literature. We performed a theoretical assessment of one specific IS fashion: crowdsourcing. The main objective of our research is to understand the characteristics of theories in crowdsourcing research and to determine the origins of these theories. Using Gregor's (2006) taxonomy, we performed a systematic literature review to identify and categorize the type of theories developed and used in crowdsourcing research. Close to forty percent of the surveyed articles are explanatory in nature, focusing on cause and effects relationships. Most articles use established theories to motivate research questions or hypotheses. Least common is theoretical research to motivate the design of crowdsourcing related artifacts.