Allison Brooks Janney (born November 19, 1959) is an American actress. In a career spanning three decades, she is known for her performances across multiple genres of screen and stage. Janney has received various accolades, including an Academy Award, a British Academy Film Award, a Golden Globe Award, and seven Primetime Emmy Awards, in addition to nominations for two Tony Awards.

Born in Boston and raised in Dayton, Ohio, Janney received a scholarship to study at the Royal Academy of Dramatic Art following her graduation from Kenyon College. After years of minor and uncredited film and television appearances, Janney's breakthrough came with the role of C. J. Cregg in the NBC political drama The West Wing (1999–2006), for which she received four Primetime Emmy Awards. In 2014, she won the Primetime Emmy Award for Outstanding Guest Actress in a Drama Series for her role as Margaret Scully on the Showtime period drama Masters of Sex. For her portrayal of Bonnie Plunkett, a cynical recovering addict on the CBS sitcom Mom (2013–2021), Janney received six Primetime Emmy Award nominations and won twice for Outstanding Supporting Actress in a Comedy Series.