The Acousto-Optic Tunable Filter (AOTF) is an electronically tuned optic filter that operates on the principle of acousto-optic diffraction in an optically anisotropic medium. It was first reported by Harris and Wallace (1) based on the collinear acousto-optic diffraction in an anisotropic medium. Later, I. C. Chang introduced a noncollinear AOTF concept (2) with a quasi -normal Bragg diffraction caused by an acousto shear wave traveling along the (110) axis in Te02 where the collinear acousto-optic interaction is not caused. Many papers reported collinear (3. 4) and noncollinear (5. 6) AOTFs and discussed the advantages and applications of them. The advantage of these devices over conventional methods of spectroscopy, prism or grating, is that its characteristics are determined by electronic signals, so that the spectrum scan rate is not limited by mechanical motions, the complete spectra can be run with a fast scan rate. Another advantage of electronic operation is that AOTF can interface very naturally with microcomputers for scan control, data collection and analysis. In addition, AOTF has large angular aperture while maintaining high spectral and imaging resolution, wide tuning range without secondary passbands. All these advantages make the AOTF potentially attractive for a variety of application. A brife theory of AOTF is presented in the first of following sections. Next, we discuss the design considerations. Then, some measured results of the performance of infrared AOTF are provied.