The 2nd International Workshop on Biomedical Image Registration (WBIR) was held June 23–24, 2003, at the University of Pennsylvania, Philadelphia. Following the success of the ?rst workshop in Bled, Slovenia, this meeting aimed to once again bring together leading researchers in the area of biomedical image registration to present and discuss recent developments in the ?eld. Thetheory,implementationandapplicationofimageregistrationinmedicine have become major themes in nearly every scienti?c forum dedicated to image processingandanalysis. Thisintenseinterestre?ectsthe?eld’simportantrolein theconductofabroadandcontinuallygrowingrangeofstudies. Indeed,thete- niques have enabled some of the most exciting contemporary developments in the clinical and research application of medical imaging, including fusion of m- timodality data to assist clinical interpretation; change detection in longitudinal studies; brain shift modeling to improve anatomic localization in neurosurgical procedures; cardiac motion quanti?cation; construction of probabilistic atlases of organ structure and function; and large-scale phenotyping in animal models. WBIR was conceived to provide the burgeoning community of investigators in biomedical image registration an opportunity to share, discuss and stimulate developments in registration research and application at a meeting exclusively devoted to the topic. The format of this year’s workshop consisted of invited talks, author presentations and ample opportunities for discussion, the latter including an elegant reception and dinner hosted at the Mutter ¨ Museum. A representation of the best work in the ?eld, selected by peer review from full manuscripts,waspresentedinsingle-tracksessions. Thepapers,whichaddressed the full diversityof registration topics, are reproduced in this volume, along with enlightening essays by some of the invited speakers.