Whereas some recent studies underline interest groups' strategy to specialize in certain venues when lobbying, we investigate under which conditions groups develop a multi-venue strategy. This study examines and compares groups' advocacy activities during three issues that were each debated in California and Switzerland. Empirical evidence shows that the policy issue at stake influences the diversity of groups that mobilize to influence an issue, while institutional factors and group types are key to explain the level of multi-venue advocacy. Multi-venue groups are propotionally more numerous in the Swiss neo-corporatist system than in the Californian pluralist system. And citizen groups are more frequently multi-venue players than business groups, regardless of the policy sector or the political system. These findings demonstrate the added value of a research design encompassing advocacy activities in all venues visited during a policy process and, furthermore, comparing these advocacy activities across political systems and policy domains.