Beginning with the concept of rocket propulsion this introduction explains the difference between a launch vehicle, a spacecraft, and a rocket engine, describing the different types of propulsion required for a space mission, according to the energy available from propellants, including chemical, electric, and nuclear rocket engines. It also describes expendable and reusable launch vehicles and crewed spacecraft. This chapter also provides a definition of space (beyond the Kármán line), differentiating cis-lunar space, interplanetary, and interstellar space. It concludes with a brief historical account of how astronautics was born and emphasizes how rocket propulsion development became the main drive to support humanity’s access to Earth orbits and made possible the first missions of direct space exploration.