The book "Galileo Galilei. The sidereal messenger and part of the preface to Kepler's Dioptric, containing the original description of Galileo's astronomical discoveries" is a unique publication that combines the work of two outstanding scientists of the Renaissance: Galileo Galilei and Johannes Kepler. This book collects textual materials containing important research and discoveries of both astronomers. Galileo's Sidereal Herald is a scientific report on the first survey of the starry sky with the help of a telescope, where the scientist describes the moons of Jupiter, as well as star groups not known before. This work became one of the revolutionary ones in the field of astronomy and physics and initiated a new stage in the development of scientific research. Part of the preface to Kepler's Dioptrics includes an original description of Galileo's astronomical discoveries, which significantly influenced the further development of the theory of planetary motion. This text is a kind of addition to the works of Kepler and the discovery of new aspects in the understanding of the cosmos. The book "Galileo Galilei. The sidereal messenger and part of the preface to Kepler's dioptrics" will be a valuable source of information for all fans of the history of science and astronomy, and will also open new horizons in the perception of the universe for readers of any age and level of knowledge.