This introduction begins by examining recent work that emphasises the fluidity across supposed definitional or categorical boundaries, especially on the grounds of devotional or spiritual expression, within early modern Protestantism. It helps to break down the idea that categorical definitions based on creed can sometimes be misleading where personal and devotional lives might be more revealing. It then moves to outlining the unifying themes, sites and concerns surrounding ‘devotional identities’ as explored across the essays in this volume. Ultimately, English Protestantism is shown to be at once segregational and social, fixed in principle yet fluid in practice.