"This volume follows my recent book on pedophilia and sexual offending against children, also published by the American Psychological Association (Seto, 2008). After that endeavor, which took almost 3 years to complete, I thought I would take a break before assuming the (satisfying) challenge of writing another book. But after a plenary talk on online offending I gave at the 2009 Association for the Treatment of Sexual Abusers (ATSA) conference in Dallas, Texas, a colleague, Jean Proulx, asked me why I was not writing a book about this topic, given the demand for knowledge about this emerging problem. That was a good question. It was clear that there was a great deal of demand because of the increasing number of cases seen by law enforcement and by clinicians; it was also clear that there was a lack of research.