There is a growing interest in intra- and interorganizational network dynamics. The central question in the latter domain is, ''How do firms choose collaborative partners given their present network configuration, their goals, and characteristics to get a strategic network position?'' We introduce actor-oriented network models as a method to describe and explain the development of interorganizational collaboration networks. The models are applied to longitudinal data about collaborative agreements within the genomics industry. © 2007 Sage Publications.