The purpose of this study is to provide a broader understanding of the Yepes ten-string guitar. Since its inception, twenty-eight years ago, no authoritative work has been published providing inferential detail which explains the concept and development of the Yepes guitar. As a result, this instrument has been, and still is, criticized by some, largely from ignorance or lack of knowledge about the instrument. In an attempt to rectify this situation and make the instrument's extended possibilities known, the author has undertaken extensive research and has interviewed, amongst others, leading international authorities associated with the Yepes ten-string guitar. As a result of these efforts, a clearer and more positive understanding of the instrument has emerged. This in turn has become the foundation on which this dissertation has been written. The opening chapter of this dissertation provides an overview, showing how the guitar emerged and developed before the concept of multi-string guitars became established in Europe, during the second half of the eighteenth century. Aspects pertaining to the early guitar's physical features, performance practices, music, tuning and stringing methods are discussed. Several multi-string vihuelas and guitars are also mentioned. The following chapter presents a survey of numerous experiments carried out during the 1770-1900 period; to 'improve' the capabilities of the guitar. Here a number of early multi-string instruments related to the Yepes ten-string guitar are discussed. These include guitars with added basses, guitars with added trebles, guitars with added basses and trebles, and guitars with multiple necks. The third chapter shows how out of an enormous variety of eccentric forms of the guitar, some professional guitarists opted for multi-string guitars (with added basses) as their instruments, whilst others preferred the six-string variety. The music of guitarist-composers who composed for multi-string guitars is discussed alongside those who wrote specifically for the six-string guitar. The rationale for the tuning and disposition of strings on most of these multi-string guitars, past and present, as well as several illustrations showing their physical features are included. The penultimate chapter comprises an interview with Narciso Yepes and other leading figures associated with the ten-string guitar. The reasons behind Yepes' unique concept for the ten-string guitar, arguments for and against the instrument, as well as its tuning and problems related to playing this instrument are discussed. The chapter includes an inquiry(with examples) showing how the ten-string guitar can be used, amongst other things, to facilitate the playing of difficult passages in music originally composed for the six-string guitar. The extension of the repertoire with music composed specifically for this instrument is also briefly discussed. A comprehensive discography of recordings made by Narciso Yepes on the ten-string guitar is presented in the appendix. A more detailed discussion of the ten-string guitar repertoire in the twentieth century is presented in the final chapter. It includes several compositions originally intended for the traditional guitar, which have become associated with the Yepes guitar. At least five compositions composed and dedicated to Narciso Yepes by various composers are also examined. It is concluded that this instrument clearly offers more than what has been assumed over the past twenty-eight years.