This book provides an in-depth and self-contained treatment of the latest advances achieved in quantitative spectroscopic analyses of the observable outer layers of stars and similar objects. Written by two leading researchers in the field, it presents a comprehensive account of both the physical foundations and numerical methods of such analyses. The book is ideal for astronomers who want to acquire deeper insight into the physical foundations of the theory of stellar atmospheres, or who want to learn about modern computational techniques for treating radiative transfer in non-equilibrium situations. It can also serve as a rigorous yet accessible introduction to the discipline for graduate students. * Provides a comprehensive, up-to-date account of the field* Covers computational methods as well as the underlying physics* Serves as an ideal reference book for researchers and a rigorous yet accessible textbook for graduate students* An online illustration package is available to professors at press.princeton.edu