This lecture covers the principles and applications of Transmission Electron Microscopy (TEM), including TEM imaging, diffraction, high-resolution TEM, Scanning TEM (STEM), and Energy-dispersive X-ray (EDX) analysis. It explores the interaction of electrons with matter, electron diffraction, image formation, contrast mechanisms, and Cs-aberration correction for HR-TEM. The lecture also delves into Electron Energy-Loss Spectroscopy (EELS), in situ TEM techniques, and electron tomography for 3D reconstructions. Various examples are provided, such as diffraction contrast imaging, Fresnel fringes, and STEM-EDX mapping. The advantages and disadvantages of in situ TEM, including straining, deformation, and mechanical manipulation, are discussed, along with the study of irradiation, melting, and solidification processes.