In this work we give a general overview on Johannes Kepler's astronomical work. We treat, in a chronological order, the four most important books related to the issue written by him, namely, the Mysterium Cosmographicum, the Astronomia Nova, The Harmony of the Worlds and Epitome of Copernican Astronomy, in order to make clear the historical stages of the development of the author's scientific thought. We tried to emphasize the rather determining presence in his thought of a philosophical-theological element and a physical conception, as well as a methodological inclination already typical of the emerging modern science. [ABSTRACT FROM AUTHOR]