Disability is complex and multifaceted, complicating governments' efforts to collect the high-quality, comprehensive data necessary for developing, implementing, and monitoring policies. Yet data are needed to obtain information on functioning in the population, to identify the population with disabilities, and to disaggregate indicators of well-being by disability to determine whether people with disabilities are participating in society to the same extent as those without disabilities. In this article we discuss the need for data harmonization to improve disability research and policy. We describe standard question sets on disability developed for inclusion in surveys and administrative systems, as well as the need for coordination of both statistical and administrative data systems. Until disability data become more harmonized, it will not be possible to support the development of comprehensive, evidence-based policies and programs to address the needs of the population with disabilities.