The Kavli Institute for Particle Astrophysics and Cosmology is designed to facilitate collaboration among theoretical and experimental physicists. Located at the Stanford Linear Accelerator Center (SLAC), the building provides research offices, laboratories, computer labs, conference meeting rooms, and a state-of-the-art auditorium. It anchors the central quad with materials and massing sympathetic to existing buildings and provides a prominent image to SLAC visitors. The sustainable, resource-efficient design integrates proper solar orientation, shading, spectrally-selective glazing, daylighting, and a mechanical system combining under-floor air distribution and natural ventilation. The plan organization and raised-access floor system allow for maximum flexibility to meet changing needs.