Lisa Oudens Monaco (born February 25, 1968) is an American attorney who served as the 39th United States deputy attorney general from 2021 to 2025. She is a member of the Democratic Party.

Monaco previously served as homeland security advisor under President Barack Obama from 2013 to 2017. In this role, she served as the chief counterterrorism advisor to the president and was a statutory member of the U.S. Homeland Security Council. Prior to this, Monaco served as associate deputy Attorney General from 2009 to 2011 and assistant attorney general for the National Security Division from 2011 to 2013. Monaco also served as acting United States Attorney General in her capacity as United States Deputy Attorney General for a couple of hours following the resignation of Merrick Garland at noon on January 20, 2025, pursuant to 28 U.S.C. § 508, until her own resignation a few hours later, with Gary M. Restaino then serving as acting Attorney General in his capacity as United States Attorney for the District of Arizona, pursuant to Executive Order 14136 titled "Providing an Order of Succession Within the Department of Justice" that was signed by President Joe Biden on January 3, 2025 and published in the Federal Register on January 13, 2025, for a few hours until President Donald Trump signed an executive order naming DOJ Chief Administrative Hearing Officer James McHenry as acting United States Attorney General later in the day on January 20, 2025.

Monaco was born in Boston, to parents Mary Lou (Oudens) and Anthony Monaco, and was raised in Newton, Massachusetts. She comes from an Italian-American family from Biccari, in the Southern Italian region of Apulia. Monaco graduated from the Winsor School in Boston in 1986. Monaco attended Harvard University, graduating with a Bachelor of Arts, magna cum laude, in American history and literature in 1990.

After earning her bachelor's degree, she worked as a research associate for The Wilson Quarterly at the Woodrow Wilson International Center for Scholars from 1990 to 1991, and as a senior associate for the Health Care Advisory Board, a healthcare advisory group, from 1991 to 1992. She was a research coordinator for the United States Senate Committee on the Judiciary, where she worked on the Violence Against Women Act, from 1992 to 1994 under then-chairman Joe Biden.

Monaco enrolled at the University of Chicago Law School, working as an intern in the White House Counsel's Office in 1996 before earning her J.D. degree in 1997. Monaco was also a summer associate for the law firm Hogan and Hartson, LLP. During her time at the University of Chicago, she spent summers working in Washington, D.C. as an intern on the D.C. Superior Court and as an intern for the United States Department of Justice in 1995. Additionally, Monaco served as the editor-in-chief of the University of Chicago Law School Roundtable, a legal journal.

Following graduation from law school, she joined the New York State Bar Association in 1998. From 1997 to 1998, Monaco worked as a law clerk for Judge Jane Richards Roth on the United States Court of Appeals for the Third Circuit, before she went on to work as counsel to then U.S. Attorney General Janet Reno from 1998 to 2001.

From 2001 to 2007, she was an assistant U.S. attorney in the United States Attorney's office for the District of Columbia, and was appointed as a member of the Justice Department's Enron Task Force, co-leading the trial team in the prosecution of five former Enron executives from 2004 to 2006. Monaco received Department of Justice Awards for Special Achievement in 2002, 2003 and 2005.

She received the Attorney General's Award for Exceptional Service for her work on the Enron Task Force, the department's highest award. After the end of the Enron trial and the Justice Department's disbandment of the special task force, Monaco worked as a special counselor to FBI Director Robert Mueller. She was later chosen by Mueller to be his deputy chief of staff and then his chief of staff, a position she held until January 2009.