The recognition of nucleic acids is one strategy by which cells can detect infectious agents. As life is ultimately determined by the existence of nucleic acids, this defence strategy has evolved in many different organisms and operates effectively in many different cell types. Here, we review the recent progress in our understanding of the molecular mechanisms by which DNA activates cells to induce inflammation and antimicrobial immunity. DNA can be detected in different cellular compartments and can induce a range of cellular responses, such as an antiviral response and pyroptotic cell death together with the maturation and release of active interleukin-1beta.