In educational assessment, educators observe what students say, do, or make in a few particular circumstances and attempt to infer what they know, can do, or have accomplished more generally. A web of inference connects the two. Some connections depend on theories and experience concerning the targeted knowledge in the domain, how it is acquired, and the circumstances under which people bring their knowledge to bear. Other connections may depend on statistical models and probability-based reasoning. Still others concern elements and processes involved in test construction, administration, scoring, and reporting. This paper describes a framework for assessment that makes explicit the interrelationships among substantive arguments, assessment designs, and operational processes. The work was motivated by the need to develop assessments that incorporate purposes, technologies, and psychological perspectives that are not well served by familiar forms of assessments. However, the framework is equally applicable to analyzing existing assessments or designing new assessments within familiar forms. (Contains 6 tables, 11 figures, and 53 references.) (Author/SLD)