This research-in-progress paper describes the factors that influence the adoption of IT platforms for application development. The adoption of specific platforms is of tremendous importance in the IT industry; as developers choose particular platforms, they influence the programming languages, applications, and technologies that will become dominant in the future. IT adoption has been a popular area of research for several decades, with a number of theoretical explanations having been developed. IT adoption, however, may differ systematically from IT platform adoption. To investigate the factors that influence IT platform adoption, and whether those factors differ from those that are relevant in IT adoption, we conduct an interpretive field study, analyzing interviews with mobile application developers. After analyzing our results, we discuss the similarities to and differences from extant research on IT adoption.