The Pacific Northwest Site Office (PNSO) is an organization within the U.S. Department of Energy's Office of Science with responsibility to oversee and manage the Management and Operating (M&O) contract for the Pacific Northwest National Laboratory (PNNL) in Richland, Washington.

PNNL is one of ten Office of Science Laboratories and is a multi-program laboratory with a primary mission on delivering breakthrough science and technology in the areas of Energy and Environment, Fundamental and Computational Science, and National Security. PNNL also performs work for the National Nuclear Security Administration (NNSA) and the Department of Homeland Security (DHS) and a host of other Federal agencies. The PNSO is responsible for program implementation, acquisition management, and laboratory stewardship at PNNL. Through its oversight role, the PNSO is affecting the safe and efficient operation of PNNL while enabling the pursuit of visionary research and development in support of DOE's missions.