Disability determination meets important societal needs, involving billions of dollars and millions of people every year. However, disability determination decisions often are incorrect, and the high proportion of decision appeals and reversals creates additional administrative expense and difficulty for the people that the disability determination system is intended to support. Projects funded by the United States Social Security Administration explored these issues and developed new conceptual models and tools to improve the accuracy and fairness of disability determination. This paper provides an introduction to the projects and the papers in this special issue of the Journal of Occupational Rehabilitation.