Аннотация:A description is given of the composition and basic structures of the interstellar medium; attention is given to the distribution of interstellar gas, gas-dust complexes and interstellar molecules, nebulae, interstellar masers, H I clouds, hot rarefied gas, gas in the Galactic center, and the balance of the momentum and mass of the interstellar gas, pertaining to gas evolution. Particular consideration is given to light nebulae; H I regions; gas-dust complexes in relation to interstellar molecules and star formation; and interstellar masers which are connected with centers of star formation.