Our research uses advanced in situ and operando electron microscopy to directly investigate gas–solid reactions and microstructural evolution under controlled environments and elevated temperatures. Using gas-cell TEM/STEM and complementary microscopy approaches, we study oxidation, corrosion, phase transformations, interface evolution, and degradation mechanisms in structural and functional materials. Experiments can be performed under controlled dry and water-vapor-containing environments, enabling us to determine how temperature, gas chemistry, and microstructure influence reaction pathways and material performance. By combining real-time imaging with analytical techniques such as STEM-EDS and EELS, we correlate nanoscale structural and chemical changes with reaction kinetics and mechanisms. These capabilities provide fundamental insight into dynamic material behavior under conditions relevant to aerospace, energy, nuclear, and other extreme-environment applications.