A collision‐less plasma is an ionized fluid that is so hot and tenuous that interactions between individual particles are unimportant. In such a plasma, electric and magnetic fields mediate interactions among particles, and fundamental physics is addressed by kinetic theories that describe not only the spatial and temporal variations of the medium, but also its velocity‐space properties.The outer corona of our Sun and the outer coronae of many stars are collision‐less plasmas. Thus, the preface of Plasma Astrophysics begins. “This textbook is intended as an introduction to the physics of solar and stellar coronae, emphasizing kinetic plasma processes.” But the content extends well beyond the stated purview. In fact, many plasmas of the universe are collision‐less, including many space plasmas—those that are subject to in situ measurements by spacecraft—and a wide variety of astrophysical plasmas. Thus, although the parameters and phenomena that characterize the collision‐less plasmas of space, the solar corona, and astrophysics are often very different, the physics in each case derives from the same fundamental kinetic plasma theory.