To what extent is citizen political participation, such as electronic or personal contact with members of Congress, stimulated by membership in organized interest groups? I use data from a nationwide survey conducted by Zogby in 2007 to assess the extent to which Americans contact congressional offices, and whether membership in more activist-oriented groups, such as citizen groups, stimulates greater rates of contact than membership in professional associations or no group membership at all. I also examine whether this group ‘effect’ on participation breaks down by the method used, low-effort electronic contact (mail, email, web-based contact pages, on-line petitions) versus high-effort contact such as personal meetings with lawmakers. I find that the role played by interest groups in facilitating communication can be substantial. In the case of members from lower socio-economic backgrounds in particular, membership in a citizen group helps compensate for lack of knowledge and resources regarding how to contact Congress.