Catalytic reactions and energy conversion and storage processes commonly involve complex solid/liquid, solid/gas, and multiphase interfaces. Their reaction behavior is governed not only by the intrinsic structures of catalysts or electrode materials, but also by the dynamic evolution of adsorbed species, interfacial water, ion transport, and local microenvironments. In situ infrared spectroscopy provides direct molecular vibrational information under reaction conditions, offering an important means to identify key intermediates, probe interfacial structures, and elucidate reaction mechanisms. To meet the growing demand for in situ characterization in catalysis and energy research, the BL01B beamline at the Shanghai Synchrotron Radiation Facility has developed several complementary techniques, including microscopic in situ electrochemical infrared spectroscopy, attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and high-/low-temperature in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This review introduces the basic principles, experimental configurations, and characteristics of these techniques, and highlights their applications in green hydrogen production, fuel cells, electrochemical carbon conversion, valorization of nitrogen-containing species, value-added conversion of small organic molecules, electro-reforming of biomass and waste, electrochemical energy storage, and photocatalysis and photothermal catalysis. These studies demonstrate that in situ infrared spectroscopy has evolved from the identification of reactants and intermediates toward the analysis of reaction pathways, interfacial water and ion behavior, active-site states, and dynamic structure–activity relationships. Finally, future developments in far-infrared–terahertz in situ electrochemical spectroscopy, nanoscale in situ infrared characterization, multimodal characterization, and artificial-intelligence-assisted spectral analysis are discussed.