Molecules and Their Spectroscopic Properties presents a comprehensive collection of geometrical and spectroscopic constants and collisional characteristics for molecules most important in applications, with data on: energy levels, fundamental vibrational frequencies, electron and proton affinities, dipole moments and polarizabilities, ionization potentials and effective cross sections for various elementary processes occurring in laboratory and astrophysical plasmas, chemical processes, and molecular lasers. Besides the tabulated and graphical material, the most important physical notations and fundamental relationships are included, too. The up-to-date reference data presented will be useful for specialists working in molecular spectroscopy, physics of molecular collisions, and laser physics.