Most work on corporate Political Action Committees (PACs) accounts for their formation or activity level in terms of market concentration and collective action dilemmas. Subsidiary concerns include the effects of regulatory burden and the firm's internal organization. However, these cross-sectional designs yield little insight into the dynamics of the process. Results of logit and event history analyses of panel data on 119 U.S. firms from 1975-84 show that changes in corporate profitability, PAC formation by other firms in a firm's board of directors interlock network, and the degree of managerial dominance of corporate governance also affect the likelihood that a firm will form a PAC. Analyses also reveal important differences in PAC formation dynamics across different types of firms, particularly in their response to PAC formation by linked firms.