Peter Mark Roget (1779-1869), of Huguenot stock, trained as a physician in Edinburgh and London, yet he was increasingly drawn to the sciences, corresponding with Erasmus Darwin, Thomas Beddoes and Humphry Davy. He practised medicine (free of charge) in London at the Northern Dispensary, which he co-founded, and lectured on physiology and medical topics. His Bridgewater Treatise, on animal and vegetable physiology, is also reissued in the Cambridge Library Collection. Roget is remembered today for the present work, first published in 1852 following his retirement from professional duties. As the preface makes clear, he had contemplated such a work for nearly fifty years. It supplies a vocabulary of English words and idiomatic phrases ‘arranged … according to the ideas which they express’. The thesaurus, continually expanded and updated, has always remained in print, but this reissued first edition shows the impressive breadth of Roget’s own knowledge and interests.