This article explains why parliamentary groups invite interest groups to the parliamentary arena. It argues, interest groups access to committees not only reflect policy-makers' needs for information, and expertise but also party preferences and institutional factors such as the type of government, parliamentary committees structure, and committee's agenda capacity.Results show interest groups access to the parliamentary arena increases under minority governments, in the case of highly conflictual issues, and when the number of permanent committees increases. Also, results demonstrate parliamentary groups invite interest organizations following different logics -problem-solving or confrontation logic-depending on the type of functions they have to perform -legislative and oversight activities-. The article uses a novel comprehensive database with information on the appearances of all interest groups in the Spanish parliament from 1996 to 2015.