This CCR Focus probes deeply into progression-free survival (PFS), the commonly used yet controversial surrogate for clinical trial endpoints. Although PFS has been used for more than 40 years in clinical trials, it is fraught with many sources of error. Guest Editor John J. Crowley along with other experts in the field identify the sources of error in PFS determination, propose strategies to limit the error, and discuss two new approaches in clinical trial methodologies.  The goal for this current Focus is to promote dialogue and thinking about PFS with the hope of expediting the movement of promising new drugs through the development pipeline. Read more about other topics by visiting the CCR Focus archives.