An initial investigation of individual differences in planning. Studying how individuals differ in their approach to planning may help us to understand the cognitive activity that underlies the development of a good plan and the factors that limit planning effectiveness, as well as producing prescriptive guidelines for improving planning. The research focuses on the analysis of thinking-aloud protocols produced by five subjects as they performed a set of errand-planning tasks, and establishes patterns of individual differences in decision category usage that correlate with planning skill. Effective planners plan at a higher level of abstraction, possess a larger repertoire of planning knowledge, and exhibit a greater degree of conscious control of their planning processes. Good and poor planners make essentially the same types of planning decisions, but good planners are more aware of tradeoffs between evaluation criteria. This research should interest cognitive scientists and practitioners concerned with improving planning.