This paper focuses on a novel phenomenon—mobile banking diffusion—to illuminate unresolved questions: whether and how rivalry adoption and market structure affect the diffusion of a new technology. Using a unique, hand-collected dataset from the iTunes Store for 2008–2012, this study provides evidence that the adoptions of mobile banking apps by local rivals spur future adoptions. This effect is particularly strong in concentrated markets, where banks compete on non-price attributes. These results are robust to the application of instrumental variables that address the possibility that adoptions are merely simultaneous reactions to the same common forces.