The review discusses the role of mTOR signaling in T cell fate decisions, focusing on its regulation and function. mTOR, a conserved kinase, integrates immune signals and metabolic cues to control T cell homeostasis and activation. Under steady-state conditions, mTOR is regulated by multiple inhibitory mechanisms, ensuring normal T cell homeostasis. Antigen recognition triggers mTOR activation, which programs T cells into distinct lineages. The review highlights the importance of mTOR in T cell metabolism, where naive T cells use glucose, fatty acids, and amino acids for ATP generation. mTOR exists in two complexes, mTORC1 and mTORC2, with distinct functions. mTORC1 is sensitive to rapamycin and is regulated by the TSC1-TSC2 complex, while mTORC2 is relatively resistant to rapamycin. mTOR signaling is activated by immune activation signals, environmental stimuli, and metabolic cues. The review also discusses the role of mTOR in T cell homeostasis, where negative regulators like PTEN, TSC1, and LKB1 enforce normal T cell homeostasis. mTOR is crucial for T cell differentiation, particularly in the development of effector and regulatory T cells. mTORC1 promotes the differentiation of effector T cells and inhibits the generation of regulatory T cells, while mTORC2 is required for T helper 2 cell differentiation. The review further explores the metabolic regulation of mTOR, including fatty acid oxidation and glucose metabolism, and its role in T cell trafficking. Finally, the review discusses the therapeutic implications of targeting mTOR in T cells, particularly in the context of cancer and autoimmune diseases.The review discusses the role of mTOR signaling in T cell fate decisions, focusing on its regulation and function. mTOR, a conserved kinase, integrates immune signals and metabolic cues to control T cell homeostasis and activation. Under steady-state conditions, mTOR is regulated by multiple inhibitory mechanisms, ensuring normal T cell homeostasis. Antigen recognition triggers mTOR activation, which programs T cells into distinct lineages. The review highlights the importance of mTOR in T cell metabolism, where naive T cells use glucose, fatty acids, and amino acids for ATP generation. mTOR exists in two complexes, mTORC1 and mTORC2, with distinct functions. mTORC1 is sensitive to rapamycin and is regulated by the TSC1-TSC2 complex, while mTORC2 is relatively resistant to rapamycin. mTOR signaling is activated by immune activation signals, environmental stimuli, and metabolic cues. The review also discusses the role of mTOR in T cell homeostasis, where negative regulators like PTEN, TSC1, and LKB1 enforce normal T cell homeostasis. mTOR is crucial for T cell differentiation, particularly in the development of effector and regulatory T cells. mTORC1 promotes the differentiation of effector T cells and inhibits the generation of regulatory T cells, while mTORC2 is required for T helper 2 cell differentiation. The review further explores the metabolic regulation of mTOR, including fatty acid oxidation and glucose metabolism, and its role in T cell trafficking. Finally, the review discusses the therapeutic implications of targeting mTOR in T cells, particularly in the context of cancer and autoimmune diseases.