How do religious parties with historically elite support bases win the mass support required to succeed in democratic politics? This dissertation examines why the world's largest such party, the upper-caste, Hindu nationalist Bharatiya Janata Party (BJP) has experienced variable success in wooing poor Hindu populations across India. Briefly, my research demonstrates that neither conventional clientelist techniques used by elite parties, nor strategies of ideological polarization favored by religious parties, explain the BJP's pattern of success with poor Hindus. Instead the party has relied on the efforts of its "social service" organizational affiliates in the broader Hindu nationalist movement. The dissertation articulates and tests several hypotheses about the efficacy of this organizational approach in forging party-voter linkages at the national, state, district, and individual level, employing a multi-level research design including a range of statistical and qualitative techniques of analysis. In doing so, the dissertation utilizes national and author-conducted local survey data, extensive interviews, and close observation of Hindu nationalist recruitment techniques collected over thirteen months of fieldwork.