This article reviews our work on ab initio studies of molecular structure and spectroscopy of gas phase molecular complexes. The ab initio calculations were performed at the Hartree-Fock level with extended polarized plus diffuse functions basis sets, and also including electronic correlation effects using distinct approaches. The basis set superposition error (BSSE) is taken into account using the counter poise method. The preferred minimum energy structures are found to be well described by the theoretical methods. Harmonic frequencies and intensities of vibrational normal modes are calculated and effects due to the mechanical and electrical anharmonicities are considered. An assessment of experimental approaches commonly used for evaluating stabilization energies of weakly bound complexes is also made.