The Society was established in name on 4 August 1962 at Pontarddulais in South Wales, but did not have a constitution until 18 May 1963. The formation was at least partly inspired by the annual BBC Wales Radio Lecture given on the 13 February 1962 by Saunders Lewis and entitled Tynged yr iaith (The fate of the language).
The Society's first public protest took place in October 1962 at Pont Trefechan in Aberystwyth, where around forty members and supporters held a 'sit-in' blocking road traffic for half an hour.
The first campaigns were for official status for the language, with a call for Welsh-language tax returns, schools, electoral forms, post office signs, birth certificates and so on. This was done through the formation of 'cells', the first operating in Bangor in April 1963 by Owain Owain who also founded and edited the Society's only publication, Tafod y Ddraig ('The Dragon's Tongue') and logo.
Cymdeithas yr Iaith believes in non-violent direct action and in the course of their campaigns over a thousand people have appeared before the courts for their part in various campaigns, many receiving prison sentences, making it one of Britain's largest protest groups since the suffragettes - in terms of fines and the numbers sent to prison. Typical actions include painting slogans on buildings owned by businesses, and other minor criminal damage. At the beginning of the 1970s Cymdeithas began to campaign for a Welsh language radio and television service. Radio Cymru was established in 1977, but in 1979 the Conservative government announced in that it would not keep its election promise of the establishment of a separate Welsh language television channel. Some protesters refused to buy television licenses and others climbed up television masts and invaded television studios.. S4C was finally launched in 1982.
Cymdeithas is a largely voluntary movement, which also employs two full-time members of staff at its head office in Aberystwyth, Ceredigion, one member in its Caernarfon office and one part-time member in the Llanfihangel ar Arth office.
The principal campaigns can be divided into six major areas:
Cymdeithas are pressing for more politicians to use Welsh in the chamber of the National Assembly for Wales, where both Welsh and English are spoken.