This synthesis study is intended to inform state aviation agencies, airport operators, stakeholders, and policy makers about Airport System Planning Practices. The report reviews literature and provides results of surveys of state aviation agencies and regional planning organizations to determine the extent to which they are involved in airport system planning, the type of studies they perform, and how successful their efforts have been in meeting the process objectives. Barbara Fritsche, Wilbur Smith Associates, Cincinnati, Ohio, collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand.