Iron Age religion in Britain — the beliefs and practices that organized communities’ relationships with the supernatural world — is poorly understood by modern standards, because Iron Age communities in Britain did not leave written records, and the physical traces of religious practice are often ambiguous or difficult to distinguish from other kinds of activity.

What is known comes from several sources: the physical archaeological evidence of deposits and structures associated with ritual activity, the classical textual sources that describe Celtic religious practices (with all their biases and inaccuracies), and the comparative anthropological literature on religious practice in cultures at broadly similar levels of social organization.

Classical sources — Roman and Greek writers who had contact with or heard accounts of Celtic peoples — describe a religious world involving druids, seasonal festivals, sacred groves, and various forms of offering to supernatural powers, including the deposition of objects in water and the sacrifice of animals and occasionally humans.

The reliability of these accounts is contested, and many modern archaeologists approach them with significant skepticism, particularly where they align with Roman stereotypes about the barbarism of Celtic peoples or where they reflect obvious misunderstandings of practices the writers had not directly witnessed.