In the United States of America，non-governmental organizations are usually called nonprofits. Most of American nonprofits have federal tax-exempt status. The total number of nonprofits is estimated at least 2 million. These organizations can be classified into four big categories：the economic interest group，the citizen interest group，the public-serving group and the international affairs group. The largest group is the public-serving one and the nonprofits belonging to this group are prestigious 501（C）（3）charities. The foundation of the interrelations between the American government and nonprofit sector is a comprehensive legal framework. The most important components of that framework are the First and Fourteenth Amendments of U.S. Constitution and associated Supreme Court decisions，federal Internal Revenue Code and related state laws. Nonprofits can influence the public policy procedure through various legal ways. The federal and state governments are the main players regarding the lawful regulation and inspection of nonprofits，and they are also the key supporters of sustainable development of nonprofit sector.