Ultraluminous X-ray sources (ULXs) that are located in external galaxies exhibit X-ray luminosities exceeding hundreds or even thousands times those of the brightest black holes in Milky Way and Local Group galaxies. New classes of objects have been discovered: ultraluminous X-ray pulsars (ULXPs) and high-velocity outflows whose X-ray-range speed is up to 0.2 c. The ULXs and ULXPs fully correspond to concepts of the super-Eddington accretion. Five ULXs exhibit in the X-range power spectra quasi-periodical oscillations and a flat-topped noise. Optical spectra of the ULXs are very similar to those of SS433, late nitrogen stars (WNL/WR) or LBV stars (luminous blue variables). The results obtained suggest that the ULXs are the systems that contain supercritical accretion disks.