The cognitive, social, and behavioral profile of the symptoms of autism spectrum disorder (ASD) is complex and heterogeneous. Finding overarching mechanistic explanations for these wide array of symptoms is a challenging task. This chapter outlines several prevailing etiological hypotheses of autism, some of which address symptoms independently, while others theorize a unified explanation for a collection of symptoms. In this context, the following theoretical models are examined: theory-of-mind deficit, executive dysfunction, complex information processing difficulty, weak central coherence, enhanced perceptual functioning, temporal binding, social motivation, extreme male brain, Bayesian priors, and multisensory integration difficulty. These hypotheses provide different levels and magnitude of explanation for the various behavioral symptoms seen in individuals with ASD. While none of these in isolation may not be sufficient to explain ASD as a whole, these models collectively provide a comprehensive picture of this disorder.