The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations and heat. This presentation provides an overview of piezoelectric harvesting system along with the closely related sub-classes of pyroelectrics and ferroelectrics; fundamental aspect are overviewed since they provide the routes to developing novel materials and applications. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration and thermal fluctuations. Examples of modeling and manufacture of porous materials and composites for piezo- and pyro-electric harvesting are discussed where the harvesting generates power from temperature fluctuations using piezoelectric materials such as ceramics, polymers and composites.