Absorption spectroscopic diagnostics are non-invasive and provide absolute species concentrations, integrated along the radiation path. Infrared diode laser spectroscopy uses molecular vibration-rotational lines, while microwave spectroscopy looks at pure rotational lines of molecules. The sensitivity of both is high, and their high resolution permits unambiguous separation and identification of many species. We have recently used IR diode laser spectroscopy to measure CF, CF@sub 2@, and CF@sub 3@ absolute concentrations in an inductively coupled GEC etching reactor in G. Hebner's laboratory at Sandia N.L. The three species' densities were studied as functions of power and pressure in C@sub 2@F@sub 6@ and CF@sub 3@H discharges, over both blanket silicon and blanket photoresist wafers. A home built microwave spectroscopic diagnostic has similarly been used at Wisconsin to study concentrations of several species in ECR plasmas intended for deposition of silicon oxide or fluorinated silicon oxide. Gas mixtures studied are silane/oxygen and TEOS/oxygen, or these with admixture of SiF@sub 4@. Species detected by this technique include SiO, CF@sub 2@, SiF@sub 2@, SiF@super +@, and several TEOS oxidation products, e.g., methyl and ethyl alcohol, formaldehyde and acetaldehyde, and formic acid. Although in principle these two absorption spectroscopic techniques are very closely related, sometimes looking at the same molecules and even absorbing from the same quantum levels, each has its own advantages and limitations, and these will be briefly discussed here. This work was supported by National Science Foundation Grant #EEC-8721545 and by SEMATECH under contract no. 38010430.