Remote sensing in the infrared region is a very powerful technique for observing atmospheric composition, either from satellite, balloon borne or ground-based systems. However, together with an accurate radiative transfer code, the analysis and interpretation of the atmospheric spectra require good knowledge of the molecular parameters of the species of interest as well as of the interfering species. This is particularly true for the recent instruments which cover wide spectral ranges at rather high spectral resolutions with excellent signal to noise ratios. The present talk will describe spectroscopic analyses which lead to improved line positions and intensities for several molecules of stratospheric or tropospheric interest. Through these examples it will be demonstrated that improving the quality of the spectroscopic parameters leads to a better interpretation of the atmospheric spectra.