Radiation therapy (RT) is established as the primary treatment of squamous cell carcinoma of the anus. Multiple randomized trials have shown that combined modality therapy with RT, 5-fluorouracil, and mitomycin-C results in high rates of local control, disease-free survival, and sphincter preservation. However, treatment-related toxicity using conventional radiation approaches remains high and may compromise therapeutic efficacy because of prolonged treatment breaks and inability to deliver adequate radiation dose. Recent developments, including the use of PET for staging, radiation planning, and response assessment, and advanced RT planning using intensity-modulated radiation therapy (IMRT), may decrease acute and late treatment-related toxicity, provide high-dose target conformality, and permit safe radiation dose escalation. This article reviews the basic principles of IMRT and highlights current literature on these recent advances and the application of new RT techniques.