Alternative Dispute Resolution （ADR） is，among many public governance tools，a very important one in the United States. The nonprofit sector is playing multi-roles as ADR’s practitioner，promoter，researcher，professional association and exchange platform，funder，educator，and international co-operator. American nonprofits and the government agencies have been working together to resolve numerous civil disputes and conflicts in the society resulted from a fast increase of population and institutionalized wealth inequality since 1970s. The main reasons behind such a deep and comprehensive involvement in ADR can be traced back to the American historical and cultural heritage，the changes in American society and civil justice reform，the rapid growth of nonprofit sector and governmental supports to ADR. American experience as well as its lessons in ADR is valuable reference for China，which is now confronting huge challenges in social governance.