This article discusses the research strategy of theory building from cases, particularly multiple cases. Such a strategy involves using one or more cases to create theoretical constructs, propositions, and/or midrange theory from case-based, empirical evidence. Replication logic means that each case serves as a distinct experiment that stands on its own merits as an analytic unit. The frequent use of case studies as a research strategy has given rise to some challenges that can be mitigated by the use of very precise wording and thoughtful research design.