Jason Reitman (born October 19, 1977) is a Canadian-born film director, writer, producer and actor, best known for directing the films Thank You for Smoking and Juno as well as utilizing unique opening sequences.

Reitman was born in Montreal, Quebec, the first of three children of comedy director Ivan Reitman and Geneviève Robert. He has two younger sisters, Catherine and Caroline. His father, Ivan, directed the successful films Ghostbusters, Stripes, and Kindergarten Cop. Jason described his childhood self as "a loser... a movie geek... shy." In the late 1980s, Reitman began appearing in small acting parts and serving as a production assistant on his father's films. He spent time in the editing rooms of his father's movies, learning the process. Throughout his 20s, instead of accepting offers to make commercial feature films, Reitman began making his own short films and directing commercials. Although he was offered the opportunity to direct Dude, Where's My Car? on two separate occasions, he declined.

Reitman graduated from the Harvard-Westlake School in 1995 and majored in English/Creative Writing at University of Southern California. In 2004, he married writer Michele Lee, with whom he co-wrote the 2004 comedic short "Consent." The two had their first child in 2006.