To date, research on parties and research on interest groups have developed largely in parallel rather than speaking to each other.  While these two types of organizations target different stages of the policy process and thus serve different functions in democratic states, they can both be conceptualized as societal organizations that mobilize citizens while developing (at least in part) close relationships to the state, in order to feed the interests they represent into political decisions, directly or indirectly. This panel tries to bridge the divide between party and group research and presents first results from several collaborative, cross-national projects that try to integrate these two subfields in two different ways. They theorize and study the relationships between parties and groups and assess how these relationships are created, what motivates them and how they evolve over time, taking the perspectives of parties and groups into account, rather than focusing on just one side of the story. Alternatively, they treat parties and groups as two types of voluntary membership organization to compare them in the context of the same research design. Such direct comparison allows examining whether these organizations (although differing in their functional orientation) respond in a similar fashion to the challenges they face in individualized societies such as an increasingly volatile membership or growing dependency on institutional resources.