Demographic interest in the explanations of the first fertility transition has receded considerably during the last decade. Despite the empirical evidence of global convergence in fertility, there is still no consensus on the factors which explain the swiftness of the change in some contexts and its deceleration in some others. From the policy perspective, it remains pivotal to locate the factors that affect the momentum of fertility transition. In this essay the fast decline to below replacement-level period Total Fertility Rate in South India will be examined as an example of fertility transition despite slow social and/or economic development. The analysis is based on a literature review of empirical studies on the determinants of regional fertility differentials in India. Some southern states, most particularly Andhra Pradesh, manifest below replacement-level fertility (TFR 1.79) despite low average age at marriage even in Indian terms, the resilience of women’s universal marriage, and heavy reliance on a terminal family planning method, female sterilization. The case of Andhra Pradesh shows that below-replacement level fertility can occur despite slow social development, widespread poverty and gender asymmetries. Geographical and social diffusion effects are partly responsible of the speed of the decline, although they are difficult to measure or test in the level of fertility decision-making.