Tunable infrared lasers have been used in research laboratories for ultrahigh resolution spectroscopy measurements of molecular gases. While these lasers offer the potential for greatly improving instrument (e.g., laser spectrometer) performance, implementation of the instrument function is complicated by the nature of the laser source. Laser characteristics which must be considered include factors such as tuning mechanisms, spectral purity, stability and power. This talk reviews these characteristics for a variety of tunable infrared lasers including diode lasers (TDL), optical parametric oscillators (0P0), and high pressure gas lasers (HPG). Particular attention is paid to recent developments in the TDL including continuous operation at 8.5 gm wavelength at temperatures above liquid nitrogen (77°K) and high power efficiency in the 4-5 um region with output powers ~0.3 W. These developments reduce the operating complexity of TDL's and significantly increase their application potential. Spectroscopic techniques used for obtaining high resolution spectra in the 3.5 to 20 um region will be discussed and illustrated with spectra of NO, CO2, and H2O.