During a benefit concert in Paris, France, David Seville (Jason Lee) is injured. Dave must recuperate and is forced to leave to Los Angeles, California his aunt to look after the Chipmunks (Alvin, Simon and Theodore) (Justin Long, Matthew Gray Gubler and Jesse McCartney). Arrangements are also made for them to go to school of West Eastman High School. After another accident, the Chipmunks are left in the care of Tobin “Toby” Seville (Zachary Levi), the grandson of Dave’s aunt.

Meanwhile, Ian Hawke (David Cross) lives in the basement of JETT Records. Three singing female chipmunks, Brittany (Christina Applegate), Jeanette (Anna Faris) and Eleanor (Amy Poehler), also known as The Chipettes, emerge and Ian hires them as plot to get back at the Chipmunks and revive his career…