For the last decade the dominant account of the role of context in simple associative learning has been the model proposed by Rescorla and Wagner (1972; also see Wagner & Rescorla, 1972). The Rescorla-Wagner model treats context like any other conditional stimulus. Since context is always present, whenever a discrete conditional stimulus (CS) is presented on a conditioning trial, the model treats that trial as a presentation of the discrete CS plus context. The fundamental feature of the model is its assertion that the associative strengths of the various conditional stimuli, including contextual stimuli, which are present on a trial, interact to determine the outcome of that trial. More specifically, changes in the associative strengths of stimuli presented on a conditioning trial are a function of the discrepancy between the maximum associative strength supportable by the unconditioned stimulus (UCS) and the current sum of the associative strengths of all stimuli present on the trial. Consequently, when a contingency between a CS and a UCS is arranged in some context, the associative strength of the CS interacts with the associative strength of the context to determine the effect of a conditioning trial in changing both associative strengths.