SINCE the terms radical and radicalism were not in use before the nineteenth century, it may fairly be asked what they signify when applied to the mid-seventeenth century. The simplest answer is a pragmatic one: by radical I mean anyone advocating changes in state, church or society which would have gone beyond the official programme of the mainstream puritan-parliamentarians in the Long Parliament and the Westminster Assembly of Divines. In the Parliament I therefore exclude here the ‘political Independents’, alias the War Party, other than the handful of pre-1647–8 republicans. In the Assembly I exclude the ‘Five Dissenting Brethren’, who were the spokesmen of moderate Congregationalism, but outside it I include some religious Independents whose radicalism will be presently defined. To borrow another nineteenth-century figure of speech, if we look to the Left of the mainstream Puritans and Parliamentarians, what a bewildering profusion of groups and individuals appears. It is scarcely necessary to have studied the period at all to be familiar with the names of many such sects or movements, if not perhaps of all: Anabaptists, Antinomians, Behmenists, Brownists, Comenians, Diggers, Familists, Fifth-Monarchy Men, Grindletonians, Levellers, Mortalists, Muggletonians, Quakers, Ranters, Seekers, and Socinians. Yet simply to reel off such a list is to omit many interesting and remarkable groups and individuals: would-be reformers of the professions and of law, medicine and education, free-traders, agricultural improvers, philo-semites and proto-feminists, to mention only some of the most obvious. Any reader of Thomas Edwards' Gangraena and other contemporary commination or of Christopher Hill's The World Turned Upside Down and his other writings will be familiar with most of them and no doubt with others too.