John Locke (1632-1704) was a prolific correspondent and left behind him over 3,600 letters, a collection almost unmatched in pre-modern times. A man of insatiable curiosity and wide social connections, his letters open up the cultural, social, intellectual, and political worlds of the later Stuart age. Spanning half a century, they mark the transition from the era of revolutionary Puritanism to the dawn of the Enlightenment. Locke is chiefly known as a philosopher, a theorist of empiricism in his Essay Concerning Human Understanding, a theorist of liberalism in his Two Treatises of Government, and a theorist of religious toleration in his Letter concerning Toleration. But his interests extended further still, to education, medicine, finance, theology, empire, and the natural world. He was a Fellow of the early Royal Society. He received letters from scholars in Paris and Amsterdam, from colonial administrators in Virginia, from aristocrats and shopkeepers, from children, from tenants, from politicians, from philosophic women, from astronomers, chemists, and physicists. He is one of the first people whose correspondence is as far flung as North America, India, and China. A friend of Anglican archbishops and of freethinking anticlericals, of Isaac Newton and Robert Boyle, of William Molyneux the 'virtuoso' of Dublin, of Jean LeClerc of Amsterdam, and of Damaris Masham, Locke stood in the midst of the 'Republic of Letters'. This book brings together 245 of the most important and revealing letters. Half of them are letters written by Locke (twelve per cent of the total number surviving), the other half are letters written to him. If Locke's place is already secure among those who explore philosophy and political ideas, these letters will give Locke a new presence among those who are interested in the social and cultural worlds of seventeenth-century Britain.