Margo Cathleen Harshman (born March 4, 1986) is an American actress, best known for playing Tawny Dean on the Disney Channel series Even Stevens. She currently has a role on The Big Bang Theory as Sheldon Cooper's assistant, Alex Jensen, and on NCIS as Agent Timothy McGee's girlfriend, Delilah Fielding.

Harshman was born in San Diego, California. She has two older sisters, one older brother and one younger brother. Harshman lived in La Costa, San Diego County, California and attended school there until she was 12, after which she moved to Orange County, California. There she finished the rest of her schooling, first at Hewes Middle School and then at Foothill High School. She played softball for eight years but quit in favor of acting. Harshman now lives in Los Angeles.

She is related to former professional baseball pitcher Jack Harshman and former Washington State University and University of Washington basketball coach Marv Harshman.

At the age of two, Harshman was entered into beauty pageants. At 3, she was involved in dance and gymnastics. At 5, she learned to play piano, and at 8, she began acting and met her first manager. She plays guitar, piano, and bass guitar.

Harshman starred on the short-lived shows Run of the House and Center of the Universe. In 2008, she co-starred in the film Keith alongside Jesse McCartney. She starred alongside fellow Disney Channel celebrities Raven-Symoné and Brenda Song in the movie College Road Trip. Harshman appeared in an episode of Grey's Anatomy in which she played the daughter of two parents caught in an 'uncomfortable' situation. In 2009, she took on a supporting role for the horror movie remake Sorority Row. She has also been in several films which, for unknown reasons, were not released.

She is currently appearing in the hit US comedy The Big Bang Theory as Alex Jensen, the assistant of Sheldon Cooper, and popular US drama series NCIS as Delilah Fielding, the girlfriend of Timothy McGee.