The following excerpt is taken form their website:
The Secular Coalition for America is a 501(c)4 advocacy organization whose purpose is to amplify the diverse and growing voice of the nontheistic community in the United States. We are located in Washington, D.C. for ready access to government, activist partners and the media. Our staff lobbies U.S. Congress on issues of special concern to our constituency.
Our member organizations are established 501(c)3 nonprofits who serve atheists, agnostics, humanists, freethinkers and other nontheistic Americans. Their purpose in founding the coalition was to formalize a cooperative structure for visible, unified activism to improve the civic situation of citizens with a naturalistic worldview. A number of additional organizations have endorsed our mission statement.
While the Coalition was created expressly by and for nontheistic Americans, we also enthusiastically welcome the participation of religious individuals who share our view that freedom of conscience must extend to people of all faiths and of none. Accordingly, our staff works in cooperation with a variety of other organizations and coalitions where common ground exists on specific issues, and our e-mail Action Alert system is open to all who visit our site.
The Coalition is not an individual membership organization. To join a national or local group, subscribe to publications, or receive information about atheism, humanism, freethought, the secular student movement, secular children's camps, nontheistic military personnel, humanistic Judaism, or Ethical Culture, please visit the Web sites of our member organizations and those of our endorsing organizations.