Once upon a time, in 1974 to be precise, three youngsters met during the ECPR workshop at the University of Essex in England. We knew nothing of what would unfold beyond liking each other's company and sharing a commitment to using mathematical ideas to advance social science research. We stayed in contact and next met at the SOECO conference in Ljubljana in 1976. Over the years since that meeting, we got together when we could, but it was not until the Social Science Methodology conference at Dubrovnik in 1988 that the idea formed for a collaboration. At that time, Vlado and Nuša saw themselves as cluster analysts and Pat was a social network analyst. As we talked, it became clear that the two fields could be joined to mutual benefit. A shared passion and dream was born: form a synthesis of cluster analytic ideas and social network ideas. This book is a result of pursuing that passion and dream.

We owe many debts and we will try to acknowledge them here. Institutional support of various forms was critical. A Fulbright fellowship allowed Nuša to visit Pittsburgh for seven months in 1990–91, and we thank the Fulbright Commission for their support. The Universities of Ljubljana and Pittsburgh have an exchange agreement. Under that agreement, Vlado came to Pittsburgh in 1991, and we worked on our joint project. This period marked the true beginning of our professional collaboration, and we presented some results at the Sunbelt XI conference in Tampa in 1991.