The development of Open Source Software (OSS) often depends on sponsoring firms. Despite their important role, the effect of changes of control rights in these firms has yet to be explored. We study the effect of acquisitions on contributions to OSS using a matched-sample analysis of 347 OSS projects affected by an acquisition. We examine contributions by employees of the sponsoring firm and other contributors, finding acquisitions to have a negative effect. Our data reveals an enormous variation across acquisitions that can be traced back to differences in acquirers’ ability and tendency to extract resources. Our qualitative data provides further insights into the underlying mechanisms. We discuss implications for practice and for research on OSS.