Glutamine, a versatile nutrient, plays a crucial role in the survival and growth of cancer cells through its participation in energy formation, redox homeostasis, macromolecular synthesis, and signaling. This review highlights the metabolic functions of glutamine and its surprising roles in supporting the biological hallmarks of malignancy. It discusses recent efforts in imaging and therapeutics to exploit tumor cell glutamine dependence, including the development of 18F-labeled analogs for PET imaging and the use of amino acid analogs and inhibitors to target glutamine metabolism. The review also explores the variability in glutamine metabolism among different types of cancer and the challenges in predicting which tumors are most likely to respond to glutamine metabolism inhibitors. Finally, it suggests a disease-focused paradigm to integrate glutamine metabolism into the diagnosis, classification, treatment, and monitoring of cancer, with a focus on neuroblastoma as an example.Glutamine, a versatile nutrient, plays a crucial role in the survival and growth of cancer cells through its participation in energy formation, redox homeostasis, macromolecular synthesis, and signaling. This review highlights the metabolic functions of glutamine and its surprising roles in supporting the biological hallmarks of malignancy. It discusses recent efforts in imaging and therapeutics to exploit tumor cell glutamine dependence, including the development of 18F-labeled analogs for PET imaging and the use of amino acid analogs and inhibitors to target glutamine metabolism. The review also explores the variability in glutamine metabolism among different types of cancer and the challenges in predicting which tumors are most likely to respond to glutamine metabolism inhibitors. Finally, it suggests a disease-focused paradigm to integrate glutamine metabolism into the diagnosis, classification, treatment, and monitoring of cancer, with a focus on neuroblastoma as an example.