Abstract The behavior analytic theories of autism are reviewed and evidence related to the theo ries and environmental causes of autism are discussed. There is little evidence that autism is caused by deviant parenting practices. However, changing parenting practices can lead to improvements in child behavior, and functional analyses have shown that the behaviors of children with autism can be explained and treated using the principles of behavior analysis. The research lends some support for two theories. The first is that autism consists of a mismatch between the childs nervous system and the envir onment. The second is that children with autism have a special difficulty in the development of stimulus control and that is especially pronounced in the area of social behavior because the contingencies are less reliable in the social world relative to th e nonsocial. Keyw ords : etiology, behavior analytic theories, autism Introduction Autism, Aspergers Syndrome, and pervasive developmental disorder -not otherwise specified (PDD -NOS ) represent the Autism Spectrum Disorders (ASD s). Currently considered a low -incidence disability, autism is the fastest growing developmental disability (Autism Society of America, 2003). The average age of diagnosis is 3 -4 years of age (Filipek et al., 1999), however some studies suggest diagno sis is possible as early as 15 months (Klin et al., 2004), others suggest 18 to 24 months (Eaves & Ho, 2004). The importance of early identification is tied to providing intervention services. The earlier intervention services are provided, the better the outcome. Lovaas (1987, 1993) demonstrated the effectiveness of early intervention for children with autism. More recently, Harris and Handleman (2000) indicated age at which intervention is provided is a predictor of later outcome, with children younger th an 48 months benefiting from intervention more than older children. Autism includes impairment across several areas of functioning, however general descriptions will not describe all individuals with autism perfectly, as severity and symptoms are idiosy ncratic. Often referred to as the triad problems, the essential features of autism include impaired communication (verbal and gestural), social functioning, and behavioral variability (i.e., restricted and repetitive activities) that appear in the first 36 months of life (American Psychiatric Association, 2000; Wetherby et al., 2004). Other problems associated with autism include sensory and perceptual deficits, behavior problems, and intellectual disability (American Psychiatric Association, 2000; Carpen tieri & Morgan, 1996; Freeman et al., 1991; Joseph, Tager -Flushbery, & Lord, 2002; Lovaas, 2003; Scheuffgen, Happe, Anderson, & Frith, 2000; Shriver, Allen, & Matthews, 1999; Sigman, 1998). Ten to thirty -seven percent of individuals with autism have a como rbid medical condition (Rutter, Bailey, Bolton, & Le Couteur, 1994). Autism is considered a neurodevelopmental disorder (Bailey, Phillips & Rutter, 1996) that is biologically mediated. However, there is no clear mode of inheritance and no reliable biomarke rs have been identified ( Dawson, 2007). Comprehensive reviews of the evidence for genetic and biological evidence for autism have been written (e.g., Volkmar, Paul, Klin, & Cohen, 2005). The purpose of this paper is to review the behavior analytic theories of autism and evidence related to them. A review of the theories and research related to them may stimulate further research on understanding the characteristics of autism from a behavior analytic perspective, which may in turn lead to more targe ted interventions.