There has recently been calls for Information Systems (IS) researchers to revisit the dominant mode of theorizing in IS research practice, a process often reduced to “shopping” around for an appropriate theory among a diversity of competing theories. To answer this call, this paper examines the process of theory choice from a critical realist perspective, and in so doing develops guidelines for middle-range theorizing in critical realist IS research. Three steps are identified in this process, these being to (1) understand the background theories relevant to the phenomenon under investigation,(2) contrast and combine these background theories, and (3) situatedly integrate the background theories. The process is illustrated by demonstrating its use in a case study of the emergent usage of adaptive IS.