Long known as terminal degradation stations, lysosomes have emerged as sophisticated signalling centres that govern cell growth, division and differentiation. Lysosomes interface physically and functionally with other organelles, and the master regulator mechanistic target of rapamycin complex 1 kinase is activated on lysosomes in response to nutrient and growth factor inputs. Lysosomes also enable autophagy, a 'self-eating' process essential for quality control and stress adaptation. Faulty execution of lysosomal growth and catabolic programmes drives cancer, neurodegeneration and age-related diseases.