Attenuated total reflection (ATR) infrared (IR) spectroscopy is a powerful tool for investigation of solid catalysts, allowing the detection of liquid-phase products (for on-line reaction monitoring) and the investigation of species adsorbed on the catalyst, during reaction and in the presence of strongly absorbing solvents. Flat model catalysts such as metal films as well as powder catalysts can be investigated. In favorable situations, even changes of the catalyst structure can be followed. In this review, some fundamental concepts of ATR spectroscopy are summarized, and practical aspects, such as cell design and sample preparation, are discussed. The potential and limitations of the method are illustrated with examples. Furthermore, powerful techniques aimed at enhancing signal-to-noise ratios and long-term stability are described, which make use of phase-sensitive detection of periodically varying signals and accurate reference measurements. Until now, only a rather limited number of investigations have been reported that use the ATR technique to study heterogeneous catalytic reactions at solid–liquid interfaces, but the method holds good promise because it is comparatively inexpensive and versatile and can provide a large amount of information.