Using representative panel data for Switzerland, Germany, the United Kingdom, and the United States, the thesis reveals that the link between the involvement in voluntary associations and political attitudes is characterized by a continuous process of attitudinal transformation that starts well before becoming affiliated, becomes more pronounced with the duration of membership, and may even continue or not dissipate after having left an association. Most individuals join associational contexts leading them to interact with individuals similar to them to begin with, limiting the leeway for political effects. The strongest political effects take place when newcomers have some attitudinal leeway to become closer to long-term members but at the same time are not too far from them in order to be able to find a common ground to initiate politically relevant discussions. Different associational types (expressive, instrumental, or advocacy) exhibit distinctive internal logics providing political effects peculiar to each type.