The ninth season of the American sitcom The Big Bang Theory aired on CBS from September 21, 2015 to May 12, 2016. The series returned to its regular Thursday night time slot on November 5, 2015 beginning with the season's seventh episode. On March 12, 2014, The Big Bang Theory was renewed for an additional three years, extending it through the 2016–17 television season for a total of ten seasons. Laura Spencer was promoted to the main cast during this season after being a recurring cast member for two seasons.

Sara Gilbert is an American actress best known for her role as Darlene Conner on the ABC sitcom Roseanne, for which she received two Primetime Emmy Award nominations, and its spin-off, The Conners (2018–present). She is also creator and former co-host of the CBS daytime talk show The Talk and had a main role as Leslie Winkle in the second season of CBS' The Big Bang Theory, following a recurring role in the first season.