A review is given of recent investigations of generation of internal gravity waves (IGW) in the atmosphere by mesoscale turbulent motions and of IGW climatology in the mesopause region. Equations are obtained, which described IGW generation processes and calculations are made of the characteristics of IGW propagating from tropospheric turbulent sources. It is shown that the existing intensity of tropospheric wave sources is sufficient for maintenance of observed values of IGW amplitudes and energy fluxes in the upper atmosphere.