The heterogeneity in the behavioral presentation of autism spectrum disorder (ASD) may be surpassed only by the level of heterogeneity in its etiology. There are diverse pathways to the singular diagnostic outcome of ASD, and several etiological risk factors have been proposed in recent years. This review paper examines the role of inflammation as one possible etiologic factor in ASD, juxtaposed in the context of research on the role of inflammation in other psychiatric disorders. Human, animal, and postmortem studies of inflammation in ASD were surveyed, and their direct and indirect contributions to developing potential inflammation-based treatments, as well as potential preventative considerations, in ASD were reviewed. Although the mechanisms that link inflammation and ASD remain unknown, there exists a sizable multidisciplinary literature suggesting inflammation as a trans-etiological process.