Electrochemical and electrolyte-gated transistors (EGFETs and OECTs) have emerged as powerful tools for chemical and biochemical sensing, bridging the ionic and electronic domains. These transistors operate by modulating charge carrier flow through electrolyte interfaces (EGFETs) or via ion penetration into an electroactive channel (OECTs), making them highly effective for detecting pH, ions, DNA, proteins, and enzymatic activities. A growing area of interest is the development of paper-based electrochemical transistors, leveraging cellulose and nanocellulose as substrates. These materials offer unique advantages such as flexibility, biodegradability, and compatibility with cost-effective, large-scale production methods. Paper-based transistors are particularly suited for disposable biosensors and point-of-care diagnostics, addressing the need for sustainable and accessible sensing technologies. Advances in functionalizing paper substrates with conductive polymers and inorganic nanomaterials have further enhanced their stability and sensitivity, paving the way for applications in healthcare, environmental monitoring, and food safety. Beyond paper-based approaches, the chapter explores the diverse material choices, including organic semiconductors, metal oxides, and graphene derivatives, which enhance the performance of these sensors. Additionally, innovations in extended-gated and floating-gated configurations expand their potential for selective and high-sensitivity detection. By integrating low-cost, eco-friendly materials with advanced transistor technologies, EGFETs and OECTs are set to revolutionize bioelectronics, offering versatile and efficient platforms for real-time sensing.