**1. Introduction**

This chapter aims to provide background information about head and neck cancers, including their respective treatment options and radiotherapy techniques. It is divided into 4 parts. Part 1 summarizes the information about head and neck cancers and the use of radiotherapy for head and neck cancers. Part 2 introduces the intensity-modulated radiotherapy (IMRT) which is commonly used in the treatment of head and neck cancers. Part 3 reviews the planning techniques of IMRT. Finally, part 4 discusses the current challenges of head and neck cancers radiotherapy and the promises to overcome the challenges.
