This is a textually complete and comprehensively annotated edition of the poet Arthur Hugh Clough’s letters to five of the leading American poets and scholars of his day: Ralph Waldo Emerson, Charles Eliot Norton, James Russell Lowell, Francis James Child and Henry Wadsworth Longfellow, over the period 1847–1861. Fifteen of these letters have not previously been published, and those that appear in published editions are largely incomplete and unannotated. The letters in this edition have been transcribed from the original manuscripts held at the Bodleian and Houghton Libraries. They provide a great deal of valuable information about the less well-known later period of Clough’s life and have been extensively annotated to modern scholarly standards using information from primary literary and historical sources. The introduction to the thesis contextualises Clough’s visit to America and the initiation of the correspondence with his American friends, highlighting the central importance of the ‘American dimension’ to Clough’s life and work. I also discuss aspects of nineteenth-century letter-writing that have only relatively recently become the subject of critical attention, such as the impact of material factors – postage rates, steamship schedules, etc – on Clough’s transatlantic correspondence. Clough’s creation of an ‘epistolary self’ in his private letters, together with his distinctive habit of writing ‘journal-letters’ and the idea of letters as historical ‘testimony’ are the subject of detailed analysis, and I draw a number of parallels with his use of the epistolary form in his major poetry. Chapter 2 of the thesis evaluates existing ‘theories’ of annotation, reviews current practice in relation to the annotation of nineteenth-century correspondence and concludes with a reflection on my own experience of editing Clough’s letters. The absence of a definitive version of Clough’s American letters and the comprehensive introduction will make this edition an original contribution to scholarly work on nineteenth-century correspondence and poetry.