This practical new Guide on the 2010 AAIDD Intellectual Disability: Definition, Classification, and Systems of Supports manual informs clinicians, educators, policy makers, and program managers how to implement the various components of the AAIDD definition system in their specific job settings. The authors discuss the contemporary relevance of the supports-based AAIDD definition in the context of issues ranging from special education practices and IDEA mandates, to diagnosing individuals with higher IQ and conducting retroactive diagnoses. Policy makers and program managers will benefit from discussions on how the supports paradigm can improve quality outcomes, and how the current system incorporates the consensus in the field to utilize a supportsbased approach. February 2012