The emergence of HAMAS has thrust religion onto the Palestinian political stage. As a driving political force for the intifada, HAMAS initially threatened decades of Palestinian Liberation Organization (PLO) dominance within the Palestinian communities in the West Bank and Gaza strip. Although the breakthrough peace agreements, Oslo I and Oslo II, have restored the PLO's dominance, HAMAS remains an important third voice in Israeli-Palestinian relations. This chapter analyzes the explosive interactions of religion and politics between the PLO and HAMAS through an examination of the evolution of HAMAS and its protracted relations with the PLO. Although HAMAS has a discernable structure, it has remained in a constant state of flux. This evolving structure results from Israeli attempts at eliminating HAMAS and PLO efforts to absorb HAMAS members. Consequently, only the general structure and components of HAMAS have been identified. Relations between the PLO and HAMAS have gone through different phases.