In recent years the fulfillment of the inequalities established by Bell has been tested in different laboratories in the world. These inequalities make it possible to establish which of the interpretations of quantum mechanics is correct--the interpretation due to Einstein, according to which the properties of a quantum system exist as elements of physical reality irrespective of their observation, or the Copenhagen interpretation of Bohr and Fock, according to which the properties of a microscopic system described by noncommuting operators do not exist independently of the means of measurement. The experiments can be divided into three classes: experiments with optical photons, experiments with $\gamma$ rays, and experiments with nucleons. The experiments that have been performed convincingly indicate violation of Bell's inequalities. Thus, the Copenhagen interpretation of quantum mechanics and its associated principle of relativity with respect to the means of measuring the properties of a microscopic system give at the present the only description of quantum phenomena that does not contradict experiment.