The first published dictionary to contain Welsh - Dictionarium Duplex was a Latin-Welsh, Welsh-Latin dictionary and the first of its kind. This publication showcased John Davies’s lifetime study of the Welsh language, from Old Welsh poetry dating from around the sixth century down to the seventeenth century. Davies was a Renaissance scholar and these humanistic values were evident is his Dictionarium Duplex. The preface to the volume presented an interesting statement on the uniqueness of the Welsh language, its history and its place within an international linguistic context. In addition, his familiarities with the ideas of influential humanistic scholars were evident within the publication. This dictionary was aimed at, and produced for, scholars or Latinists. It was certainly not a practical resource for the ordinary Welsh-man, nor the uneducated poet. The Dictionarium Duplex came to the attention of some of Europe’s leading linguists in the seventeenth century and laid the foundations for many future Welsh linguists and scholars. It also had a great impact on lawyers and priests during that time. Its publication is considered as one of the most important events in the history of the Welsh language in the seventeenth century.