The ultimate goal of any radiotherapy is to eradicate the disease without inflicting damage on the normal tissues surrounding the tumours, which could be responsible for late treatment morbidity. To achieve this objective, the first step is to precisely select and delineate the target volumes to which a given dose will be prescribed. This step requires the use of multi-modal images from clinical examination to anatomical and molecular images. Imaging examination will be used not only to delineate the boundaries of the tumour volume, but also to assess tumour heterogeneity and, possibly, to guide a heterogeneous dose prescription (i.e. the so-called 'dose painting' approach). Last, re-imaging the patient during treatment to assess variation of the tumour volume during radiotherapy may also be performed in the framework of adaptive treatment. Over the last decade, a lot of information has been gathered on the use of multi-modal imaging for dose planning, and its potential and technical difficulties have been identified. During the lecture, the speaker will review the state-of-the-art of multi-imaging for treatment, using head and neck tumours as a paradigm, emphasising what should be considered as routine practice and what should still be viewed as research questions. © 2018 ICRP. Published by SAGE.