Plasma physics is a necessary part of our understanding of stellar and galactic structure; it determines the magnetospheric environment of the earth and other planets; it forms the research frontier in such areas as nuclear fusion, advanced accelerators, and high frequency lasers; and its applications to various industrial processes (such as computer chip manufacture) are rapidly increasing. Thus, it is a subject with a long list of scientific and technological applications.This book provides the scientific background for understanding such applications, but it emphasizes something else: the intrinsic scientific interest of the plasma state. It attempts to develop an understanding of this state, and of plasma behavior, as thoroughly and systematically as possible. Building its explanations from carefully identified physical laws, the book avoids the occasional tendency of plasma texts to present the subject in terms of a collection of ad hoc recipes. In particular, the book emphasizes the relation between the various conceptual tools used to describe plasma (such as MHD and the Vlasov equation) and their common origin in laws of nature.Thus plasma physics is displayed as a discipline that responds to certain scientific challenges in a coherent and comprehensible way. It is a discipline with a lengthening list of scientific accomplishments, a perhaps larger list of remaining mysteries, and a characteristic point of view. The book was written with the graduate student in mind, but most of the material would also fit into an upper-level undergraduate course.