The Cancer Genome Atlas profiled 279 head and neck squamous cell carcinomas (HNSCCs) to provide a comprehensive landscape of somatic genomic alterations. We find that human papillomavirus-associated (HPV) tumors are dominated by helicase domain mutations of the oncogene PIK3CA, novel alterations involving loss of TRAF3, and amplification of the cell cycle gene E2F1. Smoking-related HNSCCs demonstrate near universal loss of TP53 mutations and CDKN2A with frequent copy number alterations including a novel amplification of 11q22. A subgroup of oral cavity tumors with favorable clinical outcomes displayed infrequent CNAs in conjunction with activating mutations of HRAS or PIK3CA, coupled with inactivating mutations of CASP8, NOTCH1 and wild-type TP53. Other distinct subgroups harbored novel loss of function alterations of the chromatin modifier NSD1, Wnt pathway genes AJUBA and FAT1, and activation of oxidative stress factor NFE2L2, mainly in laryngeal tumors. Therapeutic candidate alterations were identified in the majority of HNSCC's.