Nutrient signalling is the fundamental cellular system comprising molecular pathways and mechanisms that detect and respond to variations in nutrient availability. As a central concept in cell biology, it investigates how nutrient status is transduced into intracellular signals that regulate essential cellular processes, including metabolism, growth, proliferation, autophagy, and the balance between anabolic and catabolic states. Key characteristics involve nutrient sensors, intricate protein complexes (such as those interacting with Rag GTPases and mTORC1), and downstream effectors that coordinate these responses to maintain cellular and organismal homeostasis, with its dysregulation implicated in numerous pathological conditions.