In the last three decades, the issues of energy use and consumption have become one of the most important problems of the European market of real-estate development. The UE regulates it through legislation, standards and guidelines for both design and use of buildings. This paper lists the types of low-energy buildings, in the context of the requirements necessary for their design and construction. It also describes the initial experience with the use of these objects in terms of their advantages and disadvantages. Particular effort was made to compare the obtained parameters and comfort in active and passive objects. This paper provides an overview of low energy buildings, in order to introduce a series of articles presenting researches of individual authors.