As agents of electoral mobilization, political parties occupy an important role in the social flow of political communication, and this chapter addresses several questions regarding party mobilization efforts. Whom do the parties seek to mobilize? What are the individual and aggregate characteristics and criteria that shape party mobilization efforts? What are the intended and unintended consequences of partisan mobilization, both for individual voters and for the electorate more generally? In answering these questions we make several arguments. First, party efforts at electoral mobilization inevitably depend upon a process of social diffusion and informal persuasion, and thus the party canvass serves as a catalyst aimed at stimulating a cascading mobilization process. Second, party mobilization is best seen as being environmentally contingent upon institutional arrangements, locally defined strategic constraints, and partisan divisions within particular electorates. Finally, the efforts of party organizations generate an additional layer of political structure within the electorate that sometimes competes with social structure and often exists independently from it.