Intervention for the core symptoms and comorbid conditions associated with autism spectrum disorder (ASD) primarily involves behavioral and/or cognitive behavioral therapy. This chapter reviews the relevant research for the effectiveness of these approaches across several areas. It begins with a review of the rapidly growing research focused on early intervention for young children with ASD. Next, interventions for persons on the severe end of the autism spectrum are discussed. Specifically, studies focus either on symptomatic treatment (e.g., increasing social skills) or on packages of treatments that are designed to address the range of difficulties persons with ASD display. The chapter then describes the nascent research on persons on the milder end of the spectrum—especially work on social skills training. Finally, a growing research base on treating comorbid conditions (e.g., anxiety, sleep problems) is also briefly reviewed. A theme throughout the chapter is the need to individualize treatment and the special needs of the range of persons with ASD.