Lyndsy Marie Fonseca 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.

Colleen Carlton is a fictional character from The Young and the Restless, an American soap opera on the CBS network, last portrayed by Tammin Sursok. The character was born during the March 5, 1992, episode as the daughter of Brad Carlton and Traci Abbott. After leaving the soap opera three years later, the character returned as a teenager in 2001, portrayed by Lyndsy Fonseca, who remained in the role until 2005. The following year, the role was recast with Adrianne León, who portrayed the character for a year until Sursok took over. Sursok exited the role in 2009, following the death of the character. In 2010, an uncredited actress reprised the role in a dream.