Inner disk oscillations

The RXTE observations of GRS 1915+105 have given a new impulse to the study of spectral and timing properties of the X-ray emission of black hole candidates. At variance with any other known source, GRS 1915+105 shows dramatic changes on time scales as short as a tenth of a second. These changes are associated to marked spectral changes which have been interpreted as changes of the observable inner radius of the accretion disk. I review the existing results and discuss the current evidence for such disk oscillations. Independently of the precise theoretical models, the detailed study of these fast variations can provide an extremely valuable insight on the accretion processes onto black holes. Making use of these results, I compare the properties of GRS 1915+105 with those of other black hole candidates.