Astrophysics is a branch of space science, wherein the laws of physics and chemistry are applied in order to understand the universe and its components. Spectral line shape refers to the shape of a feature observed in spectroscopy that represents an energy change in an ion, atom or molecule. The shapes and widths of spectral lines are effective instruments for absorbing and emitting gas diagnostics in various astrophysical objects. The absorption and emission lines of astrophysical objects are formed in a variety of kinematical and physical circumstances and at a distance from the observer. Data on spectral lines and their profiles is crucial for modeling, diagnostics and analysis of laser development and design, fusion plasma, and plasma produced through laser. It is also important for various plasmas in technologies such as the piercing and welding of metals by laser-produced plasma and plasma based light sources. This book provides comprehensive insights into the theory of spectral line shapes in astrophysics. Also included herein is a detailed explanation of the various roles and applications of spectral line shapes in astrophysics. This book is a vital tool for all researching and studying this area of astrophysics.