Gel-based triboelectric nanogenerators (TENGs) are promising for flexible sensing due to their excellent conductivity, mechanical tunability, environmental adaptability, and biocompatibility. This review summarizes recent advances in gel-based TENGs for flexible sensors, covering their principles, properties, and applications. The review discusses the optimization of hydrogels, organogels, and aerogels for TENGs in flexible sensing, as well as their applications in human motion sensing, tactile sensing, health monitoring, environmental monitoring, and human–machine interaction. Challenges and future directions for gel-based TENGs in flexible sensing are also addressed. Gels are three-dimensional network structures composed of particles or polymers dispersed in another medium. Depending on the solute, gels are categorized as hydrogels, organogels, or aerogels. Gel materials offer excellent conductivity, mechanical flexibility, self-healing ability, environmental adaptability, and biocompatibility, making them suitable for flexible sensing applications. Gel-based TENGs have been extensively studied, with significant progress in hydrogel-based TENGs, organogel-based TENGs, and aerogel-based TENGs. These gels have unique properties and advantages that can be modified for the development and application of various flexible triboelectric sensors. The working mechanism of gel-based TENGs involves contact electrification and electrostatic induction. The four basic working modes of TENGs are vertical contact–separation, lateral sliding, single-electrode, and freestanding tribolayer. TENGs are broadly applicable and are classified into two main categories: energy harvesting and sensing. TENGs efficiently use dispersed low-frequency energy sources such as biomechanical, wind, ocean, and water wave energy to achieve energy conversion and harvesting. The miniaturization ability and flexibility of TENGs offer unique advantages in sensing applications, such as human motion, biomechanics, and human–computer interfaces. Gel materials have been optimized for TENGs in flexible sensing applications. Hydrogels, organogels, and aerogels have been studied for their conductivity, mechanical properties, and environmental adaptability. The conductivity of hydrogels can be enhanced by introducing conductive fillers or dopants, such as MXene nanosheets or carbonized metal–organic frameworks. The mechanical performance of hydrogels can be improved by adding nanofillers or dopants, such as ZIF-8 or Fe³+. The self-healing ability of hydrogels can be enhanced by dynamic chemical and physical bonding, such as dynamic covalent bonds or hydrogen bonding interactions. Organogels have greater solute selectivity than hydrogels and can be used as electrode materials in TENGs. Organogels exhibit high ionic conductivity, freezing resistance, and thermal and chemical stability, providing good environmental tolerance in TENGs. Organogels can partially overcome typicalGel-based triboelectric nanogenerators (TENGs) are promising for flexible sensing due to their excellent conductivity, mechanical tunability, environmental adaptability, and biocompatibility. This review summarizes recent advances in gel-based TENGs for flexible sensors, covering their principles, properties, and applications. The review discusses the optimization of hydrogels, organogels, and aerogels for TENGs in flexible sensing, as well as their applications in human motion sensing, tactile sensing, health monitoring, environmental monitoring, and human–machine interaction. Challenges and future directions for gel-based TENGs in flexible sensing are also addressed. Gels are three-dimensional network structures composed of particles or polymers dispersed in another medium. Depending on the solute, gels are categorized as hydrogels, organogels, or aerogels. Gel materials offer excellent conductivity, mechanical flexibility, self-healing ability, environmental adaptability, and biocompatibility, making them suitable for flexible sensing applications. Gel-based TENGs have been extensively studied, with significant progress in hydrogel-based TENGs, organogel-based TENGs, and aerogel-based TENGs. These gels have unique properties and advantages that can be modified for the development and application of various flexible triboelectric sensors. The working mechanism of gel-based TENGs involves contact electrification and electrostatic induction. The four basic working modes of TENGs are vertical contact–separation, lateral sliding, single-electrode, and freestanding tribolayer. TENGs are broadly applicable and are classified into two main categories: energy harvesting and sensing. TENGs efficiently use dispersed low-frequency energy sources such as biomechanical, wind, ocean, and water wave energy to achieve energy conversion and harvesting. The miniaturization ability and flexibility of TENGs offer unique advantages in sensing applications, such as human motion, biomechanics, and human–computer interfaces. Gel materials have been optimized for TENGs in flexible sensing applications. Hydrogels, organogels, and aerogels have been studied for their conductivity, mechanical properties, and environmental adaptability. The conductivity of hydrogels can be enhanced by introducing conductive fillers or dopants, such as MXene nanosheets or carbonized metal–organic frameworks. The mechanical performance of hydrogels can be improved by adding nanofillers or dopants, such as ZIF-8 or Fe³+. The self-healing ability of hydrogels can be enhanced by dynamic chemical and physical bonding, such as dynamic covalent bonds or hydrogen bonding interactions. Organogels have greater solute selectivity than hydrogels and can be used as electrode materials in TENGs. Organogels exhibit high ionic conductivity, freezing resistance, and thermal and chemical stability, providing good environmental tolerance in TENGs. Organogels can partially overcome typical