Steve Allen is an expert in multiwavelength studies of galaxy clusters and the use of galaxy clusters as cosmological probes. His team have pioneered various aspects of astrophysical and cosmological studies with galaxy clusters, with particular emphasis on X-ray and weak lensing technqiues. For this work he was co-recipient of the 2008 Bruno Rossi Prize of the American Astronomical Society. He has co-authored more than 180 publications in leading refereed journals, which have together gathered close to 20,000 citations (Google Scholar). He is a member of the Athena Science Study Team, the Athena Wide Field Imager Consortium, the Lynx Science and Technology Definition Team, the Hitomi Science Team, the Dark Energy Survey, the Euclid Consortium, the South Pole Telescope Collaboration, the Simons Observatory, the CMB-S4 Collaboration, and serves as the Department of Energy's Point of Contact for the LSST Dark Energy Science Collaboration. Allen leads the X-ray Astronomy and Observational Cosmology group at Stanford University and heads the LSST Science Department at SLAC National Accelerator Laboratory.