This article investigates the role of power and ideology in the endogenous formation of policy networks. According to the Advocacy Coalition Framework (ACF), shared ideology (conceptualized as a system of policy-relevant beliefs and values) is the primary driver of collaboration within policy subsystems. On the other hand, Resource Dependency Theory suggests that power-seeking is an important rationale behind network structure, and that collaborative ties are formed primarily on the basis of perceived influence. Hypotheses are tested using a new method of egocentric network correlation, based on survey data of policy networks in five regional planning subsystems in California (N = 506). Results suggest that ideology is an important force behind network cohesion: Not only do policy elites systematically avoid networking with ideologically dissimilar actors but collaborative ties are also systematically formed among actors with shared beliefs. Power-seeking does not operate on a network-wide scale but may drive network formation among coalitions of ideologically similar agents.