This online imaging course covers the basic concepts, best clinical practices, and technical innovations of MR, PET, and (CB)CT imaging in the modern radiotherapy workflow. The use of imaging in radiotherapy is advancing rapidly. From MRI- and PET-based tumor delineation to online image guidance for daily adaptive treatment delivery; imaging is becoming increasingly important throughout the entire radiotherapy treatment chain. Innovations in the field of image acquisition (e.g., spectral CT, functional MRI, quantitative PET) as well as image processing (image registration, segmentation, and the use of Artificial Intelligence) are already changing the way we operate on a daily basis.