An investigation of the physical and chemical properties of nine interstellar dark clouds is reported. Observations of a variety of atomic and molecular species have been obtained and the clouds have been partially mapped in the near infrared. The observations have been compared with theoretical models of the line emission and absorption from intersteller clouds to derive many of the fundamental physical parameters. The temperatures, densities, masses, sizes, and abundances of atomic and molecular species have been determined in the nine dark clouds. Also, the variations of the density and temperature as a function of radius in the clouds have been studied.