The International Classification of Functioning, Disability, and Health is a biopsychosocial framework of health-related functioning designed to provide a unifying system for health care, social services, education, and policy sectors. Since its publication in 2001, the International Classification of Functioning has been used to guide clinical practice and research in autism and attention-deficit hyperactivity disorder. More recently, to promote its practical application, shorter versions of the International Classification of Functioning, known as Core Sets, have been developed for autism and attention-deficit hyperactivity disorder. This scoping review explored the application of the International Classification of Functioning and the International Classification of Functioning Core Sets in autism and attention-deficit hyperactivity disorder. Electronic database searches were conducted, resulting in 78 studies meeting the inclusion criteria. The results demonstrate a wide-ranging application of the International Classification of Functioning using different methods across various contexts. However, the majority of the research conducted focused on autism and primarily involved children. The review highlights that although the research implemented the International Classification of Functioning, it did not necessarily align with the underlying philosophy of the International Classification of Functioning framework, as the impact of the medical perspective still seems to influence research methodologies and interpretation. Nonetheless, the International Classification of Functioning presents opportunities to facilitate a shift from a strictly medical viewpoint on neurodevelopmental conditions to more comprehensive approaches.