High resolution Fourier transform spectra of linear molecules have evoked a great deal of interest during the last several years, which could be seen from the several hundreds of papers published in the journal on the spectra of diatomic and small linear polyatomic molecules. This book describes the advantages of FT Spectroscopy, the techniques employed in absorption and emission spectroscopy, and presents the theoretical models and formulas used in the analyses and interpretation of the spectra. The Perturbations observed in the spectra due to Fermi, Darling-Dennison, Coriolis, and other anharmonic resonances; and vibrational and rotational l-type resonances etc. are discussed with suitable examples. The types of information obtained from FT spectroscopy of two to ten atomic linear molecules, their observed transitions and spectral perturbation etc. are presented along with figures and curves.