In this special issue of Biogeochemistry, we present a cross-section of the presentations from the Third International Conference on Mechanisms of Organic Matter Stabilization and Destabilization in Soils and Sediments (SOM3), and an Introduction describing conference highlights and perspectives. The conference Chair, Jan Skjemstad, deserves high praise for organizing a successful conference, as does the host committee: Ron Smernik, Jeff Baldock, Evelyn Krull, and Kris Broos. Thanks also go to the Australian Commonwealth Scientific and Research Organization (CSIRO) and The University of Adelaide for supporting the conference. Support for time and effort spent on the special issue was kindly provided by USDA Cooperative Research, Education, and Extension Service National Research Initiative—Soil Processes Program, as well as the Northern Institute of Applied Carbon Science. Finally, Kate Lajtha, the staff of Biogeochemistry, and numerous reviewers, were quite generous with their time and expertise in producing this issue.