Organic Electrochemical Transistors (OECTs) leverage ion injection from an electrolyte into an organic semiconductor film, enabling significant advancements in biological interfacing, printed logic circuitry, and neuromorphic devices. The defining characteristic of OECTs is the coupling between electronic and ionic charges within the organic film. This review discusses the mechanism of operation, materials used, fabrication technologies, and proposed applications, while critically examining the future of OECT research and development. OECTs operate by injecting ions from the electrolyte into the organic film, changing its doping state and conductivity. The gate voltage controls ion injection, while the drain voltage induces a current proportional to the mobile charge carriers in the channel. Key materials include conducting polymers like PEDOT:PSS, which exhibit high transconductance and response times suitable for biosensing and electrophysiological recordings. OECTs offer unique advantages such as volumetric gating, flexible architecture, and compatibility with various substrates. They have been used in bioelectronics for electrophysiology, cell culture monitoring, and biosensing. In circuits, OECTs enable high-performance sensors and amplifiers, and in neuromorphic devices, they mimic brain functions with low power consumption. Future research will focus on refining models to better understand ion motion, developing materials with tailored properties, and scaling up production for practical applications. OECTs have the potential to revolutionize bioelectronics, printed electronics, and neuromorphic computing.Organic Electrochemical Transistors (OECTs) leverage ion injection from an electrolyte into an organic semiconductor film, enabling significant advancements in biological interfacing, printed logic circuitry, and neuromorphic devices. The defining characteristic of OECTs is the coupling between electronic and ionic charges within the organic film. This review discusses the mechanism of operation, materials used, fabrication technologies, and proposed applications, while critically examining the future of OECT research and development. OECTs operate by injecting ions from the electrolyte into the organic film, changing its doping state and conductivity. The gate voltage controls ion injection, while the drain voltage induces a current proportional to the mobile charge carriers in the channel. Key materials include conducting polymers like PEDOT:PSS, which exhibit high transconductance and response times suitable for biosensing and electrophysiological recordings. OECTs offer unique advantages such as volumetric gating, flexible architecture, and compatibility with various substrates. They have been used in bioelectronics for electrophysiology, cell culture monitoring, and biosensing. In circuits, OECTs enable high-performance sensors and amplifiers, and in neuromorphic devices, they mimic brain functions with low power consumption. Future research will focus on refining models to better understand ion motion, developing materials with tailored properties, and scaling up production for practical applications. OECTs have the potential to revolutionize bioelectronics, printed electronics, and neuromorphic computing.