The work of Kotoshikhin, which presents a modern description of Russia in state and civil relations, although not completely complete, is very remarkable in the heterogeneity of its content. It depicts in detail the court rites, the internal composition and administration of the state, diplomatic and judicial office work, some public and private customs. Kotoshikhin's information is very detailed and accurate, most of them are confirmed by other sources of the 17th century. All this makes the work of Kotoshikhin a very valuable source on the history of the described period. It sheds new light on medieval Russia and facilitates its study not only in the 17th century, but also in previous centuries, helps to understand some ambiguities and "dark" places in the annals, is the key to a correct understanding of many state acts of the era of Tsar Alexei Mikhailovich.