This lecture covers the history of Transmission Electron Microscopy (TEM) from its invention in 1931 by Ernst Ruska and Max Knoll to the development of aberration correction techniques. It discusses the limitations of electron lenses, such as spherical and chromatic aberrations, and the efforts to correct these aberrations over the years. The presentation also delves into the success achieved in 1997 with Cs correction, leading to significant advancements in TEM technology. Furthermore, it explores the different types of contrasts in TEM imaging, including mass-thickness contrast, diffraction contrast, phase contrast for crystalline specimens, and analytical electron microscopy for chemical contrast.