This authoritative book traces the development of Plaid Cymru's political thought from its birth in 1924–5 to the establishment of the National Assembly for Wales in 1999. Through a penetrating study of the political beliefs of its most important leaders – Saunders Lewis, Gwynfor Evans, Dafydd Elis-Thomas and Dafydd Wigley – we follow the party's emergence from the political fringe to the threshold of a devolved Wales. The development of Plaid Cymru's constitutional and economic policies are examined in detail, as well as its attitude towards the Welsh language. A vibrant discussion on the nature of nationalism and nationalist ideas locates the party's intellectual development in a broader international context. This is a book that reveals Plaid Cymru in a new and sometimes controversial light.