Piezoelectric materials have been studied for nearly a century now. Initially employed in sonar technology, piezoelectric materials now have a vast set of applications including energy harvesting, sensing and actuation, and have found their way into our everyday lives. Piezoelectric material properties are being further enhanced to improve their performance and be used in novel applications. This review provides an overview of piezoelectric materials, and offers a material science and fabrication perspective on progress towards the development of practical piezoelectric energy harvesters and sensors. Piezoelectric materials have been divided into the three following classes for this review: ceramics, polymers and composites. The prominent materials under each class are examined and compared, with a focus on their linear piezoelectric response in the d33 mode. The three classes of piezoelectric materials are also compared qualitatively for a range of metrics, and the applications that each material class are best suited for is discussed. Novel piezoelectric materials such as ferroelectrets and nanogenerator devices are also reviewed here. It is shown that ceramic piezoelectric materials have strong piezoelectric properties but are stiff and brittle, whereas polymer piezoelectric materials are flexible and lightweight but do not exhibit very good piezoelectric performance. Composite materials are concluded to possess the advantages of both ceramic and polymer materials, with room to tailor-fit properties by modifying the structure and composition.