As the dramatic increase of global energy demand results in the global warming and imminent fossil fuel shortage, sustainable energy resources, such as solar energy, wind power, biomass energy and so forth, are phasing in. building energy consumption nearly occupies 1/3-1/2 of total energy in a developed country, including space heating, cooling, hot water and electricity. These sustainable energy technologies have been gradually integrated in buildings, such as solar water heater, solar PV panels and light pipes. In addition to these technologies, architectural designs have applied energy-saving approaches, such as transparent glazing in southern facade, wind-catcher and highly-insulated materials for walls and windows. All these solutions are applied in buildings which are known eco-buildings. Eco-buildings aim at a new approach for the architectural design, novel construction and sustainable energy operation in both new and/or refurbished buildings in terms of energy efficient ways, which is based on the optimum combination of the two approaches: to reduce substantially demand for heating, cooling and lighting; to supply the most energy-efficient heating, cooling and lighting based as much as possible on sustainable energy sources. This paper introduces the concept of eco-buildings and sustainable energy applications solution. Examples of eco-buildings worldwide are introduced including the Creative Energy Homes at the University of Nottingham. Large-scale eco-building projects, i.e., eco-cities, are also introduced including Malmo city (Sweden), Masdar city (UAE) and Dongtan city (China).