The piezoelectric effect is based on the principle that certain crystalline and polymer-based materials generate electrical charge in response to mechanical stress. This property positions piezoelectric sensors as passive, reliable, and sustainable energy conversion elements in energy harvesting systems. These sensors convert ambient mechanical inputs—such as vibration, impact, and pressure—into electrical energy, playing a crucial role in micro-energy harvesting applications. In energy harvester designs, various structural configurations of piezoelectric sensors are employed. Unimorph and bimorph sensors consist of one or two piezoelectric layers bonded to a metallic or flexible substrate, operating effectively in bending modes with high sensitivity. Thin film piezoelectrics are suitable for microelectromechanical systems (MEMS) due to their low-profile form, enabling efficient integration into compact systems. Stacked piezoelectric sensors, with their multilayer structures, provide high energy density and increased power output. Flexural and cantilever piezoelectric configurations optimize displacement under vibratory conditions, enhancing energy conversion efficiency in dynamic environments. Finally, spherical piezoelectric structures are capable of responding to multidirectional mechanical excitations, making them ideal for harvesting energy from irregular or non-linear vibration sources. This chapter provides a comparative analysis of these various piezoelectric sensor types in terms of structural characteristics, material compositions, and energy harvesting performance.