Heterogeneous catalysis is essential to modern chemical engineering, chemistry, andenergy applications. While reaction mechanisms have been extensively studied underultra-high vacuum (UHV)on clean, well-defined surfaces, applying these insights underpractical conditions remains challenging. This is due to (1)the dynamic evolution ofcomplex catalyst surfaces and (2) the difficulty in detecting highly reactive, short-livedintemmediates. These challenges often lead to a "cook-and-look" approach in catalystdevelopment. In situ (operando) spectroscopy, which captures real-time structural andchemical information under working conditions, offers a powerful path forward. This talkhighlights how such techniques are used to uncover mechanisms in CO oxidation, propanedehydrogenation, and C1 coupling under realistic conditions.