Transmission electron microscopy (TEM) is the oldest imaging technique using charged particles optics. It has lateral resolution well surpassing the traditional light microscopy. Foundations and basic concepts of conventional TEM will be introduced and discussed. Examples of TEM application not only limited to imaging modes will be shown. Namely the diffraction modes of operation will illustrate the contribution. Additionally, some aspects of scanning TEM (STEM) will be presented. Details of modern TEM/STEM instrumentation equipped with lens aberration correctors resulting in the resolution down to approx. 50 pm will be discussed.