Materials with the capacity to transform mechanical stresses into electrical energy and vice versa include piezoelectric polymers and polymer composites. The chapter introduces the piezoelectric effect and discusses polymer composites, emphasizing the polymer matrix and fillers to enhance performance and tune specific materials characteristics. We illustrate the versatility of these materials by analyzing the impact of filler type, size, and distribution on the composite’s piezoelectric response and its potential applications in biomedical devices, sensors, actuators, and energy harvesting. Lastly, we discuss present issues and needed advancements, such as the development of eco-friendly piezoelectric polymers and composites, which will further promote technological development and implementation.