The beautiful and fascinating legend of the lost library of Ivan the Terrible has occupied the minds of people for several centuries and is one of the great historical secrets. Many have heard of this library, but not everyone is familiar with the details of this story. How do we know that the library actually existed? What books did she contain? Why is it considered so valuable, why has it disappeared, and what is the probability of finding it? Interest in the topic from time to time arises in periodicals, but reliable information from such sources cannot be obtained. One of the most famous and fundamental studies on the library of Ivan the Terrible is the work of the Russian historian and archaeologist S.A. Belokurov (1862-1918), written on the basis of an analysis of numerous historical sources.