The essential describes the development of stars from interstellar clouds. After summarizing the key state variables and their physical relationships, the author presents the foundation of the dynamics of interstellar clouds. He formulates conditions that lead to the formation of the precursors of our stars, known as protostars. Furthermore, the standard theory of protostar formation is explained and tested against current results from modern astrophysical research. Finally, important extensions of the standard theory are discussed, which complete the overall picture.