Spectrophysics shows how observations of atomic and molecular spectra can be related to the environment of the emitting or absorbing particles, with particular applications to astrophysics, plasma physics and atmospheric physics. The first part of the book describes the relations between the structure of atoms and simple molecules and their spectra, including complex atoms, which are not normally covered in introductory texts. The second part treats the effects of temperature, density, pressure, collisions with other particles, and so on. Much of this material is normally found only in specialized texts on astrophysics or plasma physics. The experimental methods of optical spectroscopy, from the mid-infrared to the far-ultraviolet regions, are described and compared in the last part of the book with a final chapter addressing such practical matters as wavelength and intensity calibration and signal-to-noise ratios.