The effort to conserve things is part of the human struggle with the pervasive activity of matter. For as long as people have made and kept things, they have cared for and repaired them. Today’s conservator uses a variety of tools and categories developed over the last 150 years to do this work. In the next decades, new kinds of materials and a new scale of change will pose unprecedented challenges. As conservators turn to an ever-expanding set of constituencies, collaborators, and knowledge claims to do this work, how might they reconsider their role in conserving such “active matter” and in conversations about environmental and cultural sustainability? Conserving Active Matter explores the activity of matter through objects that span five continents and range in time from the Paleolithic to the present. From the things that clothe us to those that shelter us; from things that reflect our interest in the past to those that enable its performance in the present; and from sacred objects to the profane, Conserving Active Matter envisions the work of conservation as essential for the lives of the things that sustain us.