The article examines constructive characteristics of an organ, peculiarities of its structure (architecture), ways of interaction of its parts and groups. The article also examines the functions of the instrument in cathedrals and concert halls. The instruments-predecessors of an organ are also under consideration in the article. Much attention is paid to their function in the social life of ancient states.

Key words: an organ, architecture, a cathedral, a concert hall, organs' construction.