This article examines how different political systems, institutional venues, policy sectors and group types affect interest groups’ mobilization. It compares advocacy activities between Switzerland and California, two political systems that make policy using the same four venues, including direct democracy, and across three policy issues: research on stem cells, promotion of renewable energies, and railway infrastructure. Contrary to general expectation, policy sectors explain interest group mobilization, and not the institutional context or the group type. More interest groups mobilize on re-distributive policy issues across political systems. Furthermore, overall and venue-specific levels of mobilization are higher in Switzerland, as the policy-making process is more integrated, and lower in California, where venues are institutionally independent. Finally, economic groups mobilize more than citizens groups in the executive venue, regardless of the political system or policy issue.
