As we approach the 50th Anniversary of System Dynamics, researchers and practitioners have yet to reach a consensus on the components of systems thinking or a method for measuring systems thinking in individuals. This paper reviews the state of thinking about systems thinking and researcher reports of efforts to assess systems thinking. As the foundation for developing an assessment framework to be able to determine an individualís level of system thinking, we present a review of the literature and the results of a survey administered to participants at the 2006 Systems Thinking and Dynamic Modeling for K-12 Conference, in Marlboro, Massachusetts.