Oak Ridge National Laboratory (ORNL) is an American multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by a limited liability partnership  between the University of Tennessee and Battelle Memorial Institute (UT–Battelle), as a federally funded research and development center (FFRDC) under a contract with the DOE, established in 1942 ORNL is the largest science and energy national laboratory in the Department of Energy system by size and by annual budget. ORNL is located in Oak Ridge, Tennessee, near Knoxville. ORNL's scientific programs focus on advanced materials, clean energy, neutron science, nuclear science, high-performance computing, systems biology and national security.

The laboratory is home to several of the world's top supercomputers including the world's most powerful supercomputer ranked by the TOP500, Summit, and is a leading neutron science and nuclear energy research facility that includes the Spallation Neutron Source (SNS) and High Flux Isotope Reactor (HFIR), the world’s most intense neutron source. ORNL hosts the Center for Nanophase Materials Sciences (CNMS), the BioEnergy Science Center, and the Consortium for Advanced Simulation of Light-Water Reactors (CASL).

As of fiscal year 2018 (FY18), ORNL managed $1.0B of expenditures with nearly 4,800 employees and hosting 3,200 research guests annually. Of the United States Department of Energy National Laboratories and Technology Centers systems, ORNL manages the Nation’s largest materials research portfolio and the most diverse energy portfolio including US ITER and exascale projects. ORNL published over 2,200 journal publications in 2018.