Mathematical and Computational Models of Leadership: Past and Future, J. K. Hazy, W. Millhiser, and D. Solow, in J. K. Hazy, J. Goldstein & B. B. Lichtenstein (Eds.), Complex Systems Leadership Theory (Chapter 9). Mansfield, MA: ISCE Publishing Company, Mansfield, MA, 2007. (Book Chapter) In this chapter, we examine the use of mathematical and computational models to explore leadership research. We review and synthesize all of the distinct approaches that have been used in leadership research, explore their theoretical roots and look forward into the future. As we show, the research has touched several levels of analysis, including studies that focus on individuals, dyads, groups, and the organization itself. After a brief overview of the mathematical foundations of these approaches, the findings and implications of each model are discussed. We close with a discussion of the potential for mathematical and computational methods to contribute to the new paradigm of research on leadership that is the subject of this volume.