A theory of mnemonic expertise is outlined along with findings from initial tests. The expertise belongs to a nonnal adult ( D D ) w h o developed a digit-span of 104 through extended practice. The theory describes h o w mechanisms consistent with the principles of skilled m e m o r y (Chase & Ericsson, 1982; Ericsson & Staszewski, 1989) and identified by analyses of DD's behavior, support his skill. Implemented as a computational model, the theory assumes that distinct knowledge structures mediate both DD's encoding of short segments of trial lists as elaborate, well- structured L T M representations and their retrieval in several recall tasks. Current testing investigates the model's ability to generate contextual codes, a class of patterned m e m o r y elaborations experimentally shown to improve DD's serial recall (Staszewski, 1990). Given the same lists D D received, it successfully generates over 8 0 % of the contextual codes in his verbal reports. Because successful simulation of contextual codes entails accurate simulation of operations performed by first-order coding mechanisms, results support theoretical assumptions about the knowledge underlying DD's coding operations. The model's overly powerful coding suggests that more stringent architectural constraint must be incorporated to rigorouslydemonstrate h o w skilled m e m o r y can increase working m e m o r y capacity in a normal cognitive architecture and support expertise.