Neurotrophins are a family of proteins initially identified as survival factors for sensory and sympathetic neurons. They have since been shown to control various aspects of neuronal survival, development, and function in both the peripheral and central nervous systems. Each of the four mammalian neurotrophins (nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF], neurotrophin-3 [NT-3], and neurotrophin-4 [NT-4]) activates one or more members of the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB, and TrkC) and the p75 neurotrophin receptor (p75NTR). Through these receptors, neurotrophins activate multiple signaling pathways, including Ras, phosphatidylinositol-3 (PI3)-kinase, phospholipase C-γ1, and MAP kinases. P75NTR activation results in the activation of nuclear factor-κB (NF-κB) and Jun kinase. Neurotrophins play crucial roles in controlling the number of surviving neurons, regulating cell fate decisions, axon and dendrite growth, and the expression of proteins essential for neuronal function. In the adult nervous system, neurotrophins control synaptic function, plasticity, and neuronal survival. Recent studies have also revealed roles for neurotrophins outside the nervous system, such as in cardiac development, neovascularization, and immune system function. Genetic disorders associated with mutations in neurotrophins or their receptors have been linked to sensory perception, cognition, and behavioral abnormalities. The review focuses on the signaling pathways stimulated by neurotrophins that affect cell survival, differentiation, and function within the nervous system.Neurotrophins are a family of proteins initially identified as survival factors for sensory and sympathetic neurons. They have since been shown to control various aspects of neuronal survival, development, and function in both the peripheral and central nervous systems. Each of the four mammalian neurotrophins (nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF], neurotrophin-3 [NT-3], and neurotrophin-4 [NT-4]) activates one or more members of the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB, and TrkC) and the p75 neurotrophin receptor (p75NTR). Through these receptors, neurotrophins activate multiple signaling pathways, including Ras, phosphatidylinositol-3 (PI3)-kinase, phospholipase C-γ1, and MAP kinases. P75NTR activation results in the activation of nuclear factor-κB (NF-κB) and Jun kinase. Neurotrophins play crucial roles in controlling the number of surviving neurons, regulating cell fate decisions, axon and dendrite growth, and the expression of proteins essential for neuronal function. In the adult nervous system, neurotrophins control synaptic function, plasticity, and neuronal survival. Recent studies have also revealed roles for neurotrophins outside the nervous system, such as in cardiac development, neovascularization, and immune system function. Genetic disorders associated with mutations in neurotrophins or their receptors have been linked to sensory perception, cognition, and behavioral abnormalities. The review focuses on the signaling pathways stimulated by neurotrophins that affect cell survival, differentiation, and function within the nervous system.