A thorough analysis of the Plaid Cymru Party of Wales. This is the first book to discuss the development of the political thought of Plaid Cymru from its foundation to the dawn of the twenty-first century when the party emerged as the main opposition party in the devolved Senedd. It provides a chronological overview of Plaid Cymru's ideological development by focusing on the influence of the party's leaders in three different periods: Saunders Lewis, Gwynfor Evans, and the era of the two Dafydds (Wigley and Elis-Thomas). The book discusses tensions and disagreements within the party during each of these periods as well as the ideas and influence of other leading figures. In doing so, the book challenges much of the received wisdom about the party as well as its key thinkers. Widely lauded at the time of its original publication in Welsh as the most authoritative account of Plaid Cymru, its appearance in English is sure to be widely welcomed.