Transmission electron microscopy (TEM) is a powerful analytical tool used to observe the microstructure and composition of materials at the atomic or molecular level. In the field of cement and concrete research, TEM provides critical insights into the nanoscale arrangement of cement hydrates, the morphology of supplementary cementitious materials, and the nature of microstructural changes that occur over time or under stress. By transmitting a beam of electrons through ultra-thin samples, TEM allows researchers to visualize the arrangement of atoms and detect phases that are crucial for understanding the hydration processes, the formation of microcracks, and the effects of environmental degradation on concrete.