The use of operando spectroscopic tools in heterogeneous photocatalysis has experienced a strong drive in recent years. When using operando tools we must, however, consider carefully the fraction of the system to be probed in an in situ cell, that is, the volume under the simultaneous influence of excitation light and the reactants. This is not an obvious task for certain spectroscopies, particularly for those attempting to characterize the physico-chemical state of the catalysts. Herein we provide an analysis of this point applied to spectroscopies such as XAS (X-ray absorption spectroscopy) and complete the analysis of operando tools with those aimed to characterize the surface of the photocatalysts (XPS; X-ray photoelectron spectroscopy) as well as those spectroscopies, such as infrared or Raman, focusing on the study of the reactantÀcatalyst interface.