Conformal radiation therapy represents a new challenge for radiation oncologists. It offers the prospect of either increasing the radiation dose to target tissues while delivering a similar dose to organs at risk, or reducing the dose to organs at risk while maintaining the dose to target tissues. However, achievement of these objectives requires appropriate selection and delineation of clinical target volumes for different tumour sites, and this is the focus of the present book. Special emphasis is placed on the lymph node areas at risk for microscopic infiltration, addressing the question of which of these areas should be included in the target volumes. Each chapter comprehensively reviews all available data from clinical, radiological and pathological examination as well as the pattern of locoregional relapse, and offers recommendations for the selection of the clinical target volumes. Then, based on a three-dimensional description of the anatomical regions where the areas at risk are located, guidelines for the delineation of the clinical target volumes are proposed. To help the reader, two chapters on descriptive anatomy and anatomical radiology on CT/MRI slices have been included. The data presented should enable the reader to make appropriate decisions regarding the selection and delineation of the target volumes when confronted with the most frequent tumor types and sites. Interestingly, all of the debated issues are relevant irrespective of the irradiation technique used. Even for less sophisticated irradiation techniques, proper selection and delineation of clinical target volumes is of the utmost importance. It is the belief of the editors that this book will contribute in paving the way for more effective radiation oncology in the twenty-first century.