The course provides basic knowledge in a compact form about the new Code of Practice IAEA TRS 483 standard for the clinical dosimetry of small regular and irregular photon radiation fields, as they are used in stereotactic and fluence-modulated radiation therapy (IMRT), rotational radiation (e.g. VMAT, tomotherapy) and high-energy gamma and photon radiation. The focus is on the application of the standard in clinical practice. Among other things, recommended measuring methods with reference ionization chambers and suitable calibrated detectors as well as important correction factors are presented. On the basis of real examples, typical problems in the dosimetry of small fields are shown and suitable solutions are discussed. As such, it is very well suited for medical physicists who want to update and extend their skills and knowledge of practical dosimetry.