Built environment represents the man-made surroundings providing setting for human activity and so encompasses places and spaces that were created or modified by people including buildings, parks, and transportation systems. Despite the multiple benefits for living people, built environments of today are created through usage of large amounts of energy and materials, affecting the health of humans and the natural environment in negative manners. This aspect is amplified by built environments enhancing because of urban areas expanding to meet necessities and requirements of an increasing number of citizens. The built environment is responsible for both consumption of resources and energies, the generation of wastes and the emission of greenhouse gases and other pollutants, with the consequent environmental impacts. Buildings contribute hugely to those environmental issues and impacts. Therefore, life cycle evaluations upon the energy and environmental performance of buildings are desirable to find room for improvement. In this context, this chapter highlights the importance and usefulness not only of life cycle assessment but also of guiding and regulating its application in buildings, so to contribute, in turn, to enhancement of the subject literature and knowledge.