An earlier version of this paper was presented at the Xl World Congress of Sociology, New Delhi, India, in August 1986. We gratefully acknowledge the involvement of Howard Aldrich, Glenn Carroll, and Paul DiMaggio at the initial stages of our research program on voluntary organizations in metropolitan Toronto. Specific thanks are due to Howard Aldrich and James G. March for insightful comments on an earlier draft. We would specially like to thank Agnes Meinhard for outstanding statistical support and anonymous ASQ reviewers for helpful suggestions. This research was supported by grant number 410-84-0632 from SSHRC, Canada, and grant number 4555-55-7 from the National Welfare Grants Directorate, Health and Welfare, Canada. This study explores whether an ecological, an adaptation, or a random organizational action perspective more appropriately describes the impact of organizational change in a population of voluntary social service organizations. The results indicate that some changes are disruptive, some have no impact on organizational mortality, and others are adaptive. One plausible interpretation of the results is that the effects of organizational changes depend on the location of the changes in the organization -whether in the core or the periphery. Core changes, which are thought to be more disruptive, are best described by an ecological view. Peripheral changes are best described by an adaptation view. The study shows that selection and adaptation are complementary rather than contradictory views, and one clear implication is the need for simultaneous modeling of selection and adaptation processes to build a more complete theory of organizational change.