Children with disabilities, their families, and the social workers who provide services are faced with navigating complex social and institutional environments in their quest for developmental, educational and daily living supports. Models of disabilities provide conceptual frameworks for understanding and action that can inform the decision-making process of parents and social workers. A new ecological model of disability, the systems model, is proposed that integrates the medical model, focused on individual deficits, the social model, focused on disabling social environments, and the transactional model, focused on person-environment interactions. Diagnostic, institutional, and practice implications of the new model are discussed. © 2004, Taylor & Francis Group, LLC. All rights reserved.