Abstract: The paper considers the contemporary review of internal waves on a shelf based on thirty year’s experience of studying internal waves in Russian Seas. The frequency spectra of internal waves are presented and analyzed in shallow-water seas, with those waves being generated by different sources. A strong variability in the spectra differs from the Gurret-Munk one. The main processes which are enumerated lead to the generation of intense internal waves on a shelf. The characteristic features of the observed waves are described, including those of the second mode. Wide possibilities of the acoustic Doppler current profiler (ADCP) are demonstrated for studying internal waves in a sea.