This study examines the adoption of business-to-consumer (B2C) e-commerce by bricks-and-mortar companies comprising the Standard & Poor's 500 (S&P 500) listings between 1992 and 2003. B2C represents a Type III information systems (IS) innovation that integrates IS with core business technologies. Extant studies on Type III innovations have examined organizational and institutional factors, solely or collectively, in explaining adoption, but not how their effects change under shifting environments over time. We develop an integrated model comprising organizational factors (i.e., espoused values and resources) and institutional factors (i.e., normative and mimetic pressures), as well as the moderating influence of shifting environments (i.e., early period and late period demarcated by changes in the environment). Using a piecewise event-history model specification, we examine the adoption of B2C innovations by 93 organizations over time. Our results show that both organizational and institutional factors influence B2C adoption; however, their effects varied with the environmental shifts. Specifically, senior IS executives influenced adoption in the early period whereas bandwagon mimetic pressures and business norms influenced adoption in the late period. The findings of our research demonstrate the importance of explicitly modeling environmental shifts in theorizing organizational adoption of innovations.