Problem behavior is a primary barrier to successful community inclusion for people with developmental disabilities and therefore a major priority for intervention efforts. Recently, researchers and clinicians have begun to focus on the systematic assessment of a broad range of contextual variables that purportedly affect problem behavior. In the study presented in this article, the authors began developing a comprehensive, user-friendly inventory to aid primarily in the initial assessment of contextual variables and secondarily in identification of factors relevant to enhancing the reliability of contextual assessment. Forty community residence staff completed the Contextual Assessment Inventory for 20 adults with developmental disabilities. Results indicated that the CAI was efficient, comprehensive, and comprehensible. A high proportion of its items had significant test-retest reliability, but only a modest proportion had significant interrater reliability. Pragmatic reasons for lower interrater reliability are explored, and research issues pertaining to establishing the validity of contextual inventories, enhancing their reliability, and extending their use to planning interventions are discussed. (Contains 4 tables.)