The research presented in this paper is concerned with the planning component of project management and describes the use of interviewing techniques to develop cognitive models of planning for project management systems. Interviews were conducted with six project managers from six different problem domains. Protocol analysis was used to develop two types of cognitive models: process models that provided detailed descriptions of planning actions; and a higher level model of the planning process based on the Hayes-Roth theoretical model of planning. A visual representation of the planning process, called DMAP, was created to identify the type of planning that occurs at each stage of the planning process in project management. The discussion focuses on the use of cognitive models in the design of knowledge-based systems for project management.