The Celtic League, American Branch (CLAB) is founded in New York City on October 11, 1974.

The Celtic League is a pan-Celtic organisation, founded in 1961, that aims to promote modern Celtic identity and culture in Ireland, Scotland, Wales, Brittany, Cornwall and the Isle of Man – referred to as the Celtic nations. It places particular emphasis on promoting the Celtic languages of those nations. It also advocates further self-governance in the Celtic nations and ultimately for each nation to be an independent state in its own right. The Celtic League is an accredited non-governmental organization (NGO) with roster consultative status to the United Nations Economic and Social Council (ECOSOC).

The present Celtic League grows out of various other pan-Celtic organisations, particularly the Celtic Congress, but with a more political emphasis. Previously, Hugh MacDiarmid and others had suggested something along the same lines.

The Celtic League is started at the 1961 National Eisteddfod of Wales, which is held at Rhosllannerchrugog near Wrexham in northeast Wales. Two of the founding members are Gwynfor Evans and J. E. Jones, who are respectively president and secretary-general of the Welsh nationalist political party Plaid Cymru at the time. Interest is expressed by Scottish parties, and also by Breton nationalists.

There are six main, national branches of the Celtic League in the six Celtic countries, generally known by the Celtic language names of their countries: Ireland is known as Éire, Scotland as Alba, Wales as Cymru, Brittany as Breizh, Cornwall as Kernow and the Isle of Man as Mannin or Mann.

The Celtic League, American Branch (CLAB) is one of various diaspora branches, all of whom play little part in the annual general meetings. American author and linguist Alexei Kondratiev serves as president of the Celtic League, American branch. The CLAB prints its own quarterly newsletter, Six Nations, One Soul, which provides news of branch activities and events within the Celtic communities in the United States, publishes letters from members, and reviews books and recordings of Celtic interest. CLAB publishes at least six issues of a larger semi-annual magazine, Keltoi: A Pan-Celtic Review, from 2006 to 2008. CLAB also produces a wall calendar each year, with art from members, appropriate quotations, and anniversaries. Publication ceases with the 2008 issue.