The benefit of coupling in situ spectroscopic methods (attentuated total reflectance-infrared spectroscopy (ATR-IR), Raman, and UV−vis) for the real-time monitoring of homogeneously catalyzed reactions is exemplarily demonstrated on selected examples of use. In this context, the different mode of catalyst action in reduction reactions of imides and amides with phenylsilanes will be discussed. In the iron-catalyzed decomposition of formic acid, different intermediate iron complexes were identified and the inhibiting effect of chloride onto active iron complex formation could be elucidated. Furthermore, it could be shown that in a Lewis acid catalyzed cyclocondensation reaction, the reactant activation proceeds differently with AlCl 3 and TiCl 4 . For the described in situ spectroscopic studies, a versatile setup was used which allows the simultaneous registration of ATR-IR, UV−vis, and Raman spectra in small volumes of solution at different reaction-determined conditions using fiber-optic probes for the each spectroscopy.