With the advent of infrared fiber-optics components which are capable of transmission over the wavelength range 1 to 12 μ, there is a need for reliable techniques for evaluating their performance at these wavelengths. The optical properties, i.e., spectral transmittance, radiation characteristics, and image quality, of cylindrical and conical fibers are presented. An evaluation approach is evolved, based on the radiation pattern and spectral transmission profile measurements, and the concept of “characteristic curves” is introduced. Results of measurements on oxide-glass fibers (0.4–5 μ) and arsenic sulfur glass fibers (1–12 μ) are presented.