A clear picture of the dynamic relationship between the host immune system and cancer is emerging as the cells and molecules that participate in naturally occurring antitumour immune responses are being identified. The interferons (IFNs) — that is, the type I IFNs (IFNα and IFNβ) and type II IFN (IFNγ) — have emerged as central coordinators of tumour–immune-system interactions. Indeed, the decade-old finding that IFNγ has a pivotal role in promoting antitumour responses became the focus for a renewed interest in the largely abandoned concept of cancer immunosurveillance. More recently, type I IFNs have been found to have distinct functions in this process. In this Review, we discuss the roles of the IFNs, not only in cancer immunosurveillance but also in the broader process of cancer immunoediting.