Political parties play a central role in the democratic process. The academic literature contains two very different interpretations, derived from different notions of what constitutes a party and what we should examine to assess the state of parties. These lead to corresponding differences in interpretations of what role parties are playing in responding to voters and changing social conditions. The chapter provides an overview of the two very different interpretations of parties that exist in the literature. The instigation to offer new interpretations began in response to changes emerging in the 1960s. Most voters had strong affective or emotional attachments to political parties, and those attachments were stable. In the first part of the century voting had been focused on parties, and parties had the resources to respond in order to maintain this situation. The change in the issue content of politics had disrupted political alignments.