Corporate social commitment (CSC) and corporate environmental commitment (CEC) are often combined under the general rubric of corporate social responsibility. Although the two sets of activities are similar, they are also very different. Both CSC and CEC respond to issues raised by stakeholders, but CEC tends to be more "technical". This characteristic demands that CEC fit with the organization, which exposes greater economic opportunities than CSC. As a result, we argue that the extent to which these practices are implemented differs across firms over time. We analyze the extensiveness of implementation of CSC and CEC across 266 firms from 1991 to 2003, using latent growth curve modeling and one-way ANOVA. We find that firms moved towards at least a moderate level of CSC over time, but tended to bifurcate in the extent to which they implemented CEC practices, towards either the high or low end of the scale, over time. In this paper, we contribute to the institutional analysis of practice diffusion by examining how the characteristics of different kinds of practices shape the extensiveness of firm adoption patterns. As well, this research also speaks to corporate social responsibility researchers, pointing to the need to sometimes discriminate between social and environmental practices.