William Bookless is an American scientist and government official who served as the acting Under Secretary of Energy for Nuclear Security from 2020 to 2021.

Bookless, who had previously served as deputy under secretary, assumed office on November 6, 2020 after the resignation of Lisa Gordon-Hagerty.

[3][4] Bookless worked as a senior physicist at the Lawrence Livermore National Laboratory for 32 years, where he specialized in nuclear security-related issues.

On May 23, 2019, Bookless was confirmed by the United States Senate to serve as principal deputy director of the NNSA.

[5][6] After Director Lisa Gordon-Hagerty resigned on November 6, 2020, Bookless assumed her position in an acting capacity.