The National Physical Laboratory (NPL) is the national measurement standards laboratory of the United Kingdom. It is one of the most extensive government laboratories in the UK and has a prestigious reputation for its role in setting and maintaining physical standards for British industry.

Founded in 1900, it is one of the oldest metrology institutes in the world. Research and development work at NPL has contributed to the advancement of many disciplines of science, including the development early computers in the late 1940s and 1950s, construction of the first accurate atomic clock in 1955, and the invention and pioneering implementation of packet switching in the 1960s, which is today one of the fundamental technologies of the Internet. The former heads of NPL include many individuals who were pillars of the British scientific establishment.

NPL is based at Bushy Park in Teddington.