This thesis explores the achievement of the contemporary Irish poet John Montague, concentrating on his major works published from the fifties to the nineties. Montague’s themes comprise not only Ireland and history, but also love, family, environment, the power and limits of poetry, the addressing of death and boyhood memories. Through close analysis of single poems and main sequences, the study attends to aesthetic, intertextual, psychological, historical and biographical issues. Its particular emphasis is on how Montague's language opens up ways of considering such issues. My readings try, therefore, to re-enact the subtle becoming and shifting that take place in individual poems and in his work as a whole. In order to illuminate the processes at work in Montague’s poetry, the chapters of the thesis are split into some that discuss themes and others that focus on volumes. Chapter one shows how Montague's concern with poetry surfaces in his work. It draws on poems from various stages in his career; the thesis also returns in subsequent chapters to Montague's addressing of poetry. The second chapter outlines Montague’s concern with exile and land in Forms of Exile and Poisoned Lands, and with family and love in A Chosen Light and Tides. Chapter three argues that Montague uses the journey as a structural device throughout The Rough Field. The fourth chapter concentrates on Montague's treatment of his family: the father in The Rough Field, A Slow Dance and The Dead Kingdom and the mother in A Slow Dance and The Dead Kingdom, which is read as the climax of Montague's return to family members. The fifth chapter analyses his main love-sequence. The Great Cloak, examines how his re-contextualisation’s of poems and use of pictorial illustration affect the reading of some love poems, and considers two love poems from Smashing the Piano. The sixth chapter demonstrates how Montague develops old and new themes in Mount Eagle and discusses how a net of crossings constitutes the collection's structural centre. The final chapter explores how in Time in Armagh Montague refines his transformation of autobiographical material into art. The analysis of Border Sick Call locates a concern with poetry itself in the late writing and brings out the sequence's shifting between the mysterious and familiar. "But in what country have we been?" is its final line, helping to define the general concern of the thesis, which is to explore the riches of the "country" mapped by Montague's poetry.