Noah E. Friedkin is Professor and former Chair of Sociology at the University of California, Santa Barbara. He is the author of A Structural Theory of Social Influence (Cambridge University Press, 1998), which received the award for Best Book in Mathematical Sociology from the Mathematical Sociology Section of the American Sociological Association, as well as articles in various scholarly journals, including The American Sociological Review, The American Journal of Sociology, Social Forces and The Administrative Science Quarterly. He is an elected member of the Sociological Research Association. Professor Friedkin's areas of research specialization are social psychology, mathematical sociology, and formal organizations. Eugene C. Johnsen is Professor Emeritus of Mathematics, former Vice Chair of Mathematics, and former Director of Summer Sessions at the University of California, Santa Barbara. His mathematical publications have appeared in such journals as the Canadian Journal of Mathematics, Linear Algebra and its Applications, Linear and Multilinear Algebra, the Journal of Algebra, Mathematische Zeitschrift, and the Journal of Combinatorial Theory, and his social science publications have appeared in such journals as Social Networks, the Journal of Mathematical Sociology, Social Science Research, Sociological Methods and Research, and Advances in Group Processes. He held a National Academy of Sciences-National Research Council Postdoctoral Research Associateship at the National Bureau of Standards and has been a principal investigator or co-investigator on grants from the National Science Foundation and the Air Force Office of Scientific Research. Professor Johnsen's research has been in the areas of linear algebra, combinatorics, social networks, and mathematical sociology.