Kathryn ("Katie") Hoff (born June 3, 1989) is an American swimmer.

She trained with Michael Phelps in Baltimore, at North Baltimore Aquatic Club, and is currently trained by Paul Yetter. She holds the American record in the 200 meter individual medley at 2:10.05. She is a strong contender for the 2008 Olympic Games in multiple events. She is best at the 200 and 400 individual medley, though Katie is a very capable swimmer in many events, ranging from any of the four 200s to the 800 free. Katie currently holds the world record in the 400 meter individual medley.

She qualified for the 2004 Summer Olympics, but had a rather disappointing showing in her first Games, placing 7th overall in the Women's 200 metre individual medley and 17th in the 400 metre medley.

At the 2005 World Aquatics Championships, she set a Championships Record for her time of 2:10.41 in the women's 200m individual medley. She received two more gold medals at the competition, one in the 400m medley and the other for the 4x200m freestyle, with teammates Natalie Coughlin, Whitney Myers, and Kaitlin Sandeno.

She retained her 200m individual medley title by winning at the 2007 World Championships setting a new championship record of 2:10.13. She also won gold and set a new WR in the 400m IM, eclipsing Yana Klochkova's the old mark of 4:33.59, with a new standard of 4:32.89. Katie's previous experience helped her use her "veteran" status to help the most experienced member of the US team, Natalie Coughlin, prepare for their world-record-setting pace in the 4 x 200 m Freestyle Relay at the 2007 FINA World Swimming Championships.

Hoff was born in Stanford, California and lives in Towson, Maryland.