The large amount of information in this title is presented in twelve chapters. The physics of small fields is explained and the potential error in delivering small fields is discussed. The challenges in absolute, reference and relative dosimetry are addressed in detail as well as the difficulties in making small field measurements. The potential errors in dose models is presented with a discussion on the necessary elements in fluence and dose calculation methods that are needed to model small collimator settings in order to achieve acceptable computational accuracy. Attention is drawn to relevant aspects of quality assurance for the treatment machine and collimating jaws. The characteristics of commercially available detectors for small field applications are summarised. The majority of the report presents established or newly proposed methodologies on the determination of dosimetric parameters (profiles, depth functions and output factors) for single narrow collimated fields. Recommendations of good working practice to be consulted and used alongside the clinical experience, scientific judgement and existing expertise are provided. The report suggests future directions and future work required to reduce uncertainty in the determination of dose in small MV photon fields.