The proliferation of nongovernmental organizations across the developing world has sparked discussions of the “NGOization” of civil society and concern that NGOs have become increasingly uniform and internally homogenous. This article explores the evolution of NGOs in Guatemala since the 1960s and finds that NGOs historically and currently respond in diverse ways to external pressures—adjusting their strategies and actively attempting to shape their environment. Comparing two microcredit NGOs, it finds in addition that old and new models combine in unique organizational contexts in distinct ways. These two findings suggest that diversity is likely to persist among NGOs.