In the early drafts of the screenplay, Greenberg was written as a man in his early 30s. Inspired by the idea of casting Ben Stiller, Noah Baumbach & Jennifer Jason Leigh rewrote the entire script and made Greenberg to be 40 years old, turning 41.
Many of the actors in this film were first better known as the siblings or children of previously famous entertainment industry professionals: Ben Stiller is the son of comedians Jerry Stiller & Anne Meara; Jennifer Jason Leigh is the daughter of actor Vic Morrow & screenwriter Barbara Turner; Jake Paltrow is the son of director Bruce Paltrow & actress Blythe Danner, and the brother of actress Gwyneth Paltrow; Juno Temple is the daughter of director Julien Temple; Dave Franco is the brother of actor James Franco; Max Hoffman is the son of actor Dustin Hoffman; Zosia Mamet is the daughter of writer David Mamet & actress Lindsay Crouse.
Original cast included Amy Adams and Mark Ruffalo. Maggie Gyllenhaal was considered for the lead role after Amy Adams dropped out.
Greenberg protests that he is not actually Jewish because his mother was Protestant. He is referring to a strict interpretation of Jewish law which holds that inherited Jewish descent is matrilineal, but that limited view is only taken by the most Orthodox Jews. Most practicing Jews in the United States belong to the Reform movement, which accepts anyone born to a Jewish parent of either gender as Jewish (as well as converts).
James Murphy: During the party scene to which Ivan drags Greenberg, for a brief few seconds, score composer James Murphy of LCD Soundsystem walks across the screen staring at his phone.