This review will be discussed the various causes of radiation failure for head and neck cancers from radiobiologic perspective and also provided a few clinical data to illustrate the basic principle. A knowledge about multiplicity of factors that may underlie failure of radiation treatment is essential for rational application of new treatment strategies. Furthermore, it is important to distinguish causes of failure that can be reduced or minimized by application of conventional treatment from one are potentially remediable by new treatment strategies, and one that are not amenable to some modification of radiotherapeutic approach.