We have developed, and are using, optical reflection and transmission mapping as a characterization tool for analyzing compositionally graded thin film combinatorial libraries. Measurements cover the spectral range of 200 nm to 25 mum. For the UV-Vis-NIR region, a multichannel fiber optically coupled CCD array-based spectrometer is used for simultaneous reflection and transmission mapping. For the IR, a Fourier transform infrared (FTIR) spectrometer is used for sequential reflection and transmission maps. Depending upon the type of library being analyzed, the measured spectra can, with appropriate modeling, be analyzed for the optical band gap, film thickness, index of refraction, plasma frequency, conductivity, carrier scattering time and color, in addition to simple reflectance and transmittance. We discuss these techniques using examples taken from our work on both transparent conducting oxides and metal nitrides for optical coatings. (C) 2003 Elsevier B.V. All rights reserved.