Porter is conducting ongoing research on the theory of clusters, or geographic concentrations of interconnected companies and institutions in a particular field. This work includes further development of cluster theory and its implications for management and public policy (see On Competition, Boston: Harvard Business School Press, 1998 and "Clusters and the New Economics of Competition," Harvard Business Review, November-December 1998). Porter is also conducting statistical research on the incidence, growth, and decline of clusters in the U.S. economy. With Claas van der Linde of St. Gallen University in Switzerland, he is also conducting a meta-study of clusters drawn from almost 350 known studies of individual clusters.