Electron microscopy in combination with image analysis is increasingly powerful in producing 3D structures of individual molecules and large macromolecular complexes that are unapproachable by other methods. Cryo-electron microscopy (cryo-EM), is a form of transmission electron microscopy where the sample is studied at cryogenic temperatures (generally below -180 °C). This course is focused on the concepts and theories behind cryo-electron microscopy and its application in structural biology.