In this interview, AIP Oral Historian Jon Phillips interviews Dr. Sean Brennan, emeritus physicist at the Stanford Synchrotron Radiation Laboratory. Brennan describes his early life in an academic family, undergraduate education at Catholic University, and graduate education under Arthur Bienenstock at Stanford University, where he began work with synchrotron radiation. He discusses his early work at SLAC with Jo Stohr on X-Ray absorption experiments, and his post-doc at Exxon. Brennan goes on to discuss the development of the facilities and research at SLAC over the course of his tenure there, as well as his work on the NASA Stardust project analyzing asteroid and comet samples. The interview concludes with a discussion of Brennans activities after retirement, including programming apps and serving as a ski patrol rescue worker.