Adaptive behavior skills are often delayed in autism spectrum disorder (ASD), and these behaviors are significantly associated with poor outcomes in adulthood, especially for autistic individuals that have no cognitive and/or language delays. Therefore, despite having the capacity to be self-sufficient, the vast majority of autistic adults fail to obtain successful levels of employment, independent living, and interpersonal relationships. Given that more than 60% of autistic individuals have intact cognition and language, adaptive behavior skills need to be appropriately assessed as part of the diagnostic process of ASD, and profiles of delays and deficits need to be accommodated throughout development. This paper provides guidelines for conducting adaptive behavior assessments as part of a comprehensive diagnostic evaluation for ASD, which is now considered standard practice. The history and definition of the construct of adaptive behavior are discussed, and considerations for the administration of various measures, interpretation of results, and translation of findings into intervention strategies are provided.