Pictorial graffiti representing ships from prehistory, protohistory and the early medieval period are frequently examined by nautical historians and archaeologists seeking information about ancient ship technology. Examples of the academic discussion and interpretation of these images may be found from the nineteenth century to the present day, in a wide range of studies. Many of these works reflect their writers' casual, even disdainful attitudes to ancient graffiti. This may be seen in their approach to the information which these images appear to contain, which may concentrate, for example, on the certain aspects of particular subjects without reference to details in their immediate or wider contexts, which may have a bearing on the images' form and meaning. In a similar vein, other writers have interpreted ancient ship graffiti using concepts of art, such as the assumption of realism of depiction, which may be inappropriate to some early visual imagery. This thesis argues that ancient ship graffiti need a more detailed and systematic interpretation as both art and artefact before their contribution to nautical history may be more reliably evaluated. In order to explore the many challenges which these graffiti offer, a multi-disciplinary approach is used, to consider aspects of the relationship between formal art and graffiti, the psychology of image making, symbolism, the philosophy of interpretation, archaeology, and the social meaning of physical context. Following these theoretical discussions, five case studies from a number of different regional and chronological groups have been chosen to provide some examples of many of the issues which were considered. It is hoped that this study demonstrates that an approach to the interpretation of ancient ship graffiti which avoids a narrow concentration on nautical technology may reveal more of their potential as evidence, not only for the form and use of early ships, but also for other aspects of life in the past.