AbstractThe Janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway controls multiple biological processes in metazoan development and tissue homoeostasis. This creates a need for tight regulatory mechanisms to ensure proper responses. The core components of the pathway, as well as many of the regulatory molecules, are conserved in evolution and thus share similarities in organisms such as humans and fruit flies. Therefore, the fruit fly provides an amenable model system for elucidating the in vivo roles of the JAK/STAT pathway and its regulators, which are challenging to demonstrate in mammalian systems. This review will focus on describing recent advances in understanding the importance of JAK/STAT signalling in Drosophila immunity.