This paper presents the results of a one-year study on mastery of assistive technology (AT). This study sought to develop a conceptual framework for talking about mastery of AT and to create an instrument for measuring individual mastery. A Delphi Study was conducted with individuals with disabilities considered to be "power users" of AT, practitioners, and researchers. Participants were asked to: identify factors that are predictors and indicators of AT mastery, determine how to measure these factors and determine criteria for each factor for the stages of AT mastery (e.g. novice, context-dependent, transitional, and power user). The resulting measure is called the Continuum of AT Mastery (CATM).