•Target volume selection and delineation for both the primary tumor and the lymph nodes are critical steps in the treatment of head and neck tumors with IMRT.•Selection and delineation are optimal when reaching the best compromise between a too tight volume that could be associated to an unacceptable rate of local recurrence, and a too large volume.•Sets of guidelines have been proposed aiming at standardizing radiotherapy practices of head and neck cancer patients. Target volume selection and delineation for both the primary tumor and the lymph nodes are critical steps in the treatment of head and neck tumors with Intensity Modulated Radiation therapy (IMRT). These steps should be based on a probabilistic approach, which is that selection and delineation will be considered as optimal when reaching the best compromise between a too tight volume that could be associated to an unacceptable rate of local recurrence, and a too large volume, which could be associated to an unacceptable rate of treatment morbidity. Failure to do so have been reported to be associated to a higher risk of loco-regional recurrences and/or morbidity after treatment. In this framework, groups of experts proposed sets of guidelines for the radiation oncology community, aiming at standardizing radiotherapy practices of head and neck cancer patients. Although in constant improvement, such guidelines have been shown to translate into more consistent treatment approaches. This review article summarizes the knowledge accumulated over the years on target volume selection and delineation and tries to reconcile the various schools of thoughts on the topic.