The macaronic (mixed-language) business texts of London for the period 1275 to 1500 present a rich source of evidence for the medieval dialect of London English. Hitherto they have been ignored because of mistaken ideas about their value: they have been viewed as bastardized forms produced by ill-educated scribes. We cannot dismiss macaronic documents as debased or degenerate without investigation, nor should we underestimate the evidence they present for the development of the English language. The contemporary importance of these documents is attested by their sheer number - it is easier today to find macaronic business documents from the late medieval period in record offices than it is to find monolingual texts. The book focuses on terminology surrounding the River Thames to present a study of the medieval dialect of London. The vocabulary survey lists many words which had previously been lost to us, and the illustrative extracts from the texts present a fascinating picture of life in medieval times on the River Thames. The author's analysis covers the orthography, phonology, and morphology of the dialect as revealed in these texts.