Danica Mae McKellar (born January 3, 1975) is an American actress, mathematics writer, and education advocate. She played Kevin Arnold's on-off girlfriend Winnie Cooper in the television series The Wonder Years.

From 2010–2013 and 2018–present, McKellar voiced Miss Martian in the animated superhero series Young Justice. In 2015, McKellar was cast in the Netflix original series Project Mc². She also appears in several television films for Hallmark Channel.

In addition to her acting work, McKellar later wrote six non-fiction books, all dealing with mathematics (as she has a bachelor's degree in math from UCLA): Math Doesn't Suck, Kiss My Math, Hot X: Algebra Exposed, Girls Get Curves: Geometry Takes Shape, which encourage middle-school and high-school girls to have confidence and succeed in mathematics, Goodnight, numbers, and Do Not Open This Math Book.