This book gives a clear and thorough description of three fascinating linguistic projects that were carried out in the seventeenth century: the philosophical languages of George Dalgarno (1661) and John Wilkins (1668), as well as the work of Leibniz in this area. These projects combined practical purposes, such as improving communication, with profound theoretical insights concerning the representation of knowledge and the nature of language. Rich in detail, this book provides all the material for a proper understanding of the workings of these schemes, while illuminating the intellectual context in which they took shape. It will be welcomed by anyone interested in the history of linguistics and philosophy of language.