Wikipedia's introduction to green building:

"Green building is the practice of increasing the efficiency with which buildings and their sites use and harvest energy, water, and materials, and reducing building impacts on human health and the environment, through better siting, design, construction, operation, maintenance, and removal — the complete building life cycle.

Green building is also sometimes known as "sustainable building" or "environmental building", although there are slight differences in the definitions. The practice of green building can lead to benefits including reduced operating costs by increasing productivity and using less energy and water, improved public and occupant health due to improved indoor air quality, and reduced environmental impacts by, for example, by lessening storm water runoff and the heat island effect.

Green building is an essential component of the related concepts of sustainable design, sustainable development and general sustainability.

Practitioners of green building often seek to achieve not only ecological but aesthetic harmony between a structure and its surrounding natural and built environment. The appearance and style of sustainable homes and buildings can be nearly indistinguishable from their less sustainable counter-parts.

Green design often emphasizes taking advantage of renewable resources, e.g., using sunlight through passive solar, active solar, and photovoltaic techniques and using plants and trees through green roofs, rain gardens, and for reduction of rainwater run-off. Many other techniques, such as using packed gravel for parking lots instead of concrete or asphalt to enhance replenishment of ground water, are used as well."

Picture from: www.kiraly.at