Flexible bioelectronic devices have gained significant attention in the biomedical field due to their wearability, biocompatibility, and diverse functionalities. Recent advancements in flexible energy harvesters have enabled these devices to operate without external batteries, offering sustainable power solutions. This review discusses the latest developments in flexible energy harvesters, their applications in wearable devices, and challenges in self-powered biomedical systems. Flexible energy harvesters are categorized into four types: biofuel cells (BFCs), mechanical energy harvesters, radio frequency (RF) energy harvesters, and solar cells. BFCs convert biochemical energy into electrical energy using enzymes or microorganisms, making them suitable for wearable power sources. They require close contact with the human body and have been integrated into temporary transfer tattoos and textile-based devices. Recent advancements have improved their power density and efficiency, enabling real-time data transmission and drug delivery. Mechanical energy harvesters, such as piezoelectric and triboelectric nanogenerators (PENGs and TENGs), convert human motion and vibrations into electrical energy. PENGs use piezoelectric materials to generate power from bending, twisting, and stretching, while TENGs utilize electrostatic induction and contact electrification. These harvesters are lightweight, flexible, and can be integrated into wearable devices for continuous health monitoring. RF energy harvesters convert radio waves into DC power using rectennas, which are efficient for powering wearable devices. Solar cells, particularly flexible and transparent ones, are also being developed for integration into bioelectronic devices, offering a sustainable energy source. Challenges in these technologies include improving energy efficiency, ensuring long-term stability, and achieving scalability for commercial applications. Despite these challenges, flexible energy harvesters hold great promise for self-powered biomedical systems, enabling continuous health monitoring and management. Future research will focus on overcoming these challenges to enhance the performance and reliability of these energy sources in wearable and biomedical applications.Flexible bioelectronic devices have gained significant attention in the biomedical field due to their wearability, biocompatibility, and diverse functionalities. Recent advancements in flexible energy harvesters have enabled these devices to operate without external batteries, offering sustainable power solutions. This review discusses the latest developments in flexible energy harvesters, their applications in wearable devices, and challenges in self-powered biomedical systems. Flexible energy harvesters are categorized into four types: biofuel cells (BFCs), mechanical energy harvesters, radio frequency (RF) energy harvesters, and solar cells. BFCs convert biochemical energy into electrical energy using enzymes or microorganisms, making them suitable for wearable power sources. They require close contact with the human body and have been integrated into temporary transfer tattoos and textile-based devices. Recent advancements have improved their power density and efficiency, enabling real-time data transmission and drug delivery. Mechanical energy harvesters, such as piezoelectric and triboelectric nanogenerators (PENGs and TENGs), convert human motion and vibrations into electrical energy. PENGs use piezoelectric materials to generate power from bending, twisting, and stretching, while TENGs utilize electrostatic induction and contact electrification. These harvesters are lightweight, flexible, and can be integrated into wearable devices for continuous health monitoring. RF energy harvesters convert radio waves into DC power using rectennas, which are efficient for powering wearable devices. Solar cells, particularly flexible and transparent ones, are also being developed for integration into bioelectronic devices, offering a sustainable energy source. Challenges in these technologies include improving energy efficiency, ensuring long-term stability, and achieving scalability for commercial applications. Despite these challenges, flexible energy harvesters hold great promise for self-powered biomedical systems, enabling continuous health monitoring and management. Future research will focus on overcoming these challenges to enhance the performance and reliability of these energy sources in wearable and biomedical applications.