Geothermal energy is defined as the heat stored in the earth's crust above 15ºC down to 10 kilometre depth. For every kilometre from the earth surface towards the centre, the temperature increases approximately 25-30ºC and is around 200ºC at a depth of 5 kilometres. This immense heat can be used for both the electrical power generation and direct heat applications. Tidal energy is a form of hydropower that exploits the movement of water caused by tidal currents or the rise and fall in sea levels due to the tides. The tide moves a huge amount of water twice each day that could provide a great deal of energy. Ocean waves represent another renewable energy source created by wind currents passing over open water. Wave energy refers to the harnessing of this tremendous energy of ocean waves. As a move towards independence from fossil fuels, geothermal and ocean energy provide clean and cost effective power to the homes, buildings and industries. Although geothermal and ocean energy are site specific and cannot be made available everywhere as solar, wind, biomass, etc., still they present fairly good choice as reliable, flexible and environment friendly renewable energy sources. The highlights of this volume are as given under: o Geothermal power generation: reserves, technology and status review o Geothermal energy: current trends and future options o Unconventional geothermal resources: features and current uses o Exploration techniques of geothermal energy o Geothermometry in exploration and exploitation of geothermal system o Analysis of productivity performance in geothermal wells o ANN approximation of geothermal aided power cycles o Optimizing design and operation of low enthalpy geothermal systems o Geothermal energy and hydrodynamic instability of phase flows o Types of geo-exchanger systems for underground heat extraction o Modelling of geothermal heat pumps for use in HVAC systems o Low enthalpy geothermal direct utilization in Albania o Geothermal resources: solution for human life o Geothermal and ocean energy o Wave energy o Wave and tidal energy o Wave energy resources in Persian gulf, gulf of Oman and Caspian sea o Wave energy potential in enclosed seas: a case study in the south-east Mediterranean sea This volume includes 19 chapters subscribed by 35 professionals/academicians and active researchers from 12 countries, namely Albania, Algeria, Australia, Canada, Greece, Iran, Iraq, Italy, Mexico, Turkey, United Kingdom and United States of America presenting an overview of the research being carried out in different parts of the world in the area of Geothermal and Ocean Energy.