Piezoelectric energy harvesters have gained significant attention due to their ability to convert ambient mechanical vibrations into electrical energy, enabling applications in environmental monitoring, wearable technologies, and powering IoT devices. This review discusses various aspects of piezoelectric energy harvesters, including structural designs, fabrication techniques, and performance optimization strategies. It covers both inorganic (e.g., ZnO, PZT, BaTiO3) and organic (e.g., PVDF) piezoelectric materials, highlighting their unique properties and applications in flexible and stretchable energy harvesting systems. The review also explores the principles of piezoelectricity, including the direct and converse piezoelectric effects, and their relationship with ferroelectricity and pyroelectricity. Key factors affecting performance, such as electromechanical coupling factor, piezoelectric coefficient, and voltage coefficient, are discussed. The review emphasizes the importance of material synthesis, device architecture, and fabrication methods in enhancing energy harvesting efficiency. It also addresses challenges in flexible energy harvesting, such as reducing screening effects through chemical doping, surface treatment, and junction effects. The review highlights recent advancements in piezoelectric materials, including 2D materials like MoS2 and organic polymers, and their potential for next-generation wearable and flexible electronics. Overall, the review provides a comprehensive overview of piezoelectric energy harvesting technologies, their applications, and future directions.Piezoelectric energy harvesters have gained significant attention due to their ability to convert ambient mechanical vibrations into electrical energy, enabling applications in environmental monitoring, wearable technologies, and powering IoT devices. This review discusses various aspects of piezoelectric energy harvesters, including structural designs, fabrication techniques, and performance optimization strategies. It covers both inorganic (e.g., ZnO, PZT, BaTiO3) and organic (e.g., PVDF) piezoelectric materials, highlighting their unique properties and applications in flexible and stretchable energy harvesting systems. The review also explores the principles of piezoelectricity, including the direct and converse piezoelectric effects, and their relationship with ferroelectricity and pyroelectricity. Key factors affecting performance, such as electromechanical coupling factor, piezoelectric coefficient, and voltage coefficient, are discussed. The review emphasizes the importance of material synthesis, device architecture, and fabrication methods in enhancing energy harvesting efficiency. It also addresses challenges in flexible energy harvesting, such as reducing screening effects through chemical doping, surface treatment, and junction effects. The review highlights recent advancements in piezoelectric materials, including 2D materials like MoS2 and organic polymers, and their potential for next-generation wearable and flexible electronics. Overall, the review provides a comprehensive overview of piezoelectric energy harvesting technologies, their applications, and future directions.