Pan-Celticism

right|thumb|200px|A Pan-Celtic Flag of two interlaced Triskelion, designed by Breton Robert Berthelier in 1950. Pan-Celticism (, Scottish Gaelic: Pan-Cheilteachas, Breton: Pan-Keltaidd, Welsh: Pan-Geltaidd, Cornish: Pan-Keltaidh, Manx: Pan-Cheltaghys), also known as Celticism or Celtic nationalism, is a political, social and cultural movement advocating solidarity and cooperation between Celtic nations (both the Brythonic and Gaelic branches) and the modern Celts in Northwestern Europe. Some pan-Celtic organisations advocate the Celtic nations seceding from the United Kingdom and France and forming their own separate federal state together, while others simply advocate very close cooperation between independent sovereign Celtic nations, in the form of Breton, Cornish, Irish, Manx, Scottish, and Welsh nationalism.

Just like other pan-nationalist movements, the pan-Celtic movement grew out of Romantic nationalism and specific to itself, the Celtic Revival. The pan-Celtic movement was most prominent during the 19th and 20th centuries (roughly 1838 until 1939). Some early pan-Celtic contacts took place through the Gorsedd and the Eisteddfod, while the annual Celtic Congress was initiated in 1900. Since that time the Celtic League has become the prominent face of political pan-Celticism. Initiatives largely focused on cultural Celtic cooperation, rather than explicitly politics, such as music, arts and literature festivals, are usually referred to instead as inter-Celtic.