Katherine Moore Porter (born January 3, 1974) is an American politician, law professor, and lawyer who is the U.S. representative from California's 47th congressional district since 2023, previously representing the 45th congressional district from 2019 to 2023. She is the first Democrat to be elected to represent the 45th district, covering much of south-central Orange County, including Irvine, Tustin, and Lake Forest along with large portions of Anaheim and Laguna Niguel. Porter was reelected in 2022 in the newly redistricted 47th congressional district.

Porter graduated from Yale University and Harvard Law School and has taught law at several universities, including the University of California, Irvine, William S. Boyd School of Law, and University of Iowa. She is deputy chair of the Congressional Progressive Caucus and has received media attention for her questioning during congressional hearings. Porter declined to seek reelection to the United States House of Representatives in 2024 and became a candidate in the 2024 United States Senate election in California, to succeed retiring incumbent Dianne Feinstein.