Valid and reliable measurement is essential to high-quality science, particularly in the context of Patient-Reported Outcome Measures (PROMs). Although some PROMs exist for individuals with intellectual disability (ID), very few are available for those with autism spectrum disorder (ASD) and other neurodevelopmental disabilities (NDD). This entry reviews international literature on these measures and quality of life (QoL) for individuals with ID, ASD, and other NDD. It aims to describe a theoretical framework for optimal assessment and support planning. Current issues in PROMs research include content and construct operationalization, measure accessibility, and validation. Barriers to research dissemination include lack of guidance, funding constraints, and challenges in collecting representative samples. A comprehensive QoL assessment should include shared, individual, and family aspects as well as integrating subjective and objective perspectives. It can address the full range of NDD, regardless of the severity and associated functional impairment. For those with profound ID, consistent behavioral repertoires could be considered as indicators of individual QoL, which can be recognized by proxies and validated by independent observers. When assessing whole-person QoL, it is essential to move beyond generic instruments that focus solely on health-related aspects. Although these tools consider the individual, they generally still align with a traditional medical perspective and focus on more specific aspects of functioning. Existing generic tools vary significantly in their conceptualizations of shared aspects of QoL, individual dimensions, and specific indicators. QoL assessment should not be aimed at categorizing people, services, or systems, but rather at providing support for a set of values that align with the viewpoints of persons with NDD. This entry concludes by emphasizing the need to improve PROMs in NDD research, including robust assessment methods, diverse samples, expanded psychometric properties, and field-specific guidelines. Overall, optimism remains high for future research and practice in this area.