It is with the greatest of sadness that we report that our valued colleague, Mark Kleiman, passed away on Sunday, July 21. We will remember Mark for his intense commitment to the work of criminal justice and drug policy reform. We will dearly miss his wit and incisive analysis. Mark mentored and collaborated with generations of leading academics and researchers. Whether writing alone or in collaboration with others, he leaves behind a rich set of clearly written and rigorously researched books, journal articles, and commentaries. Mark's ideas will live on through his written works and the scholarship of his many students and collaborators. Our thoughts are with Mark's family as well as his many friends and colleagues.