Lyndsy Marie Fonseca (born January 7, 1987) is an American actress. She began her career by appearing as Colleen Carlton on the CBS daytime soap opera The Young and the Restless, on which she starred between 2001 and 2005. Thereafter, she had a series of other recurring roles, including Penny Mosby on the CBS sitcom How I Met Your Mother, Donna on HBO's Big Love, and Dylan Mayfair on the fourth season of the ABC television series Desperate Housewives.
From 2010 to 2013, Fonseca starred as Alex Udinov on The CW's Nikita and Angie Martinelli on ABC's Marvel's Agent Carter from 2015 to 2016. Fonseca has also appeared in a variety of film roles, including Jenny in Hot Tub Time Machine (2010) and Katie Deauxma in Kick-Ass (2010) and its 2013 sequel.
Fonseca was born in Oakland, California, the daughter of Lima Lynn (née Bergmann) and James Victor Fonseca. She is partly of Portuguese descent. Her mother later married attorney Reid Dworkin, through whom Fonseca has a half-sister, Hannah Leigh Dworkin. Fonseca graduated from Barbizon Modeling and Acting School in San Francisco and relocated to Los Angeles at age 12. She soon made her screen debut as Colleen Connelly-Carlton on the soap opera The Young and the Restless.