Stressing that fully declared atheism was illegal throughout the Romantic period and beyond, the chapter gives a brief survey of some philosophical Enlightenment ‘isms’ which could sometimes be seen as connected to it, such as materialism, pantheism, necessitarianism, idealism, scepticism, and deism. It then moves from such abstractions into the world of active, sometimes dangerous debates about atheism itself, focusing on specific clashes between such figures as Joseph Priestley, Edward Gibbon, Thomas Paine, Richard Carlile, C. F. Volney, Erasmus Darwin, and their critics. The final section looks more closely at ways in which the atheism debate impinged on some of the period’s canonical poets, particularly the anxiously Christian Samuel Taylor Coleridge and the firmly atheist Percy Bysshe Shelley.