As Nigeria enters a period of potentially rapid economic growth due to the increase in the working age population, it is critical to understand why fertility remains so high there. Nigeria’s current total fertility rate (TFR) of 5.5 (0.2 fewer children per woman than the TFR of 5.7 reported in both the 2003 and 2008 NDHS surveys) is projected to continue to decline, but questions remain about whether this decline is inevitable and whether it will continue apace. Regardless, Nigeria’s population growth will continue through at least 2050 due to simple population momentum. Other challenges are the persistent and vast fertility differentials; many groups remain above replacement fertility across various social and geographical sub-units of the country. Using data primarily from the 2013 Demographic and Health Survey (DHS), as well as from 2003 and 2008 surveys, we document that many population subgroups and zones of the country are finally beginning to show signs of fertility convergence and decline. Nevertheless, some population subgroups still have higher fertility, especially: Hausa/Fulani/Kanuri women, women who live in the North West geopolitical zone, Muslim and traditionalist women, women who live in poor households, women who have lower levels of education, women who are opposed to family planning, women who marry early, and women who give birth early. In order for the projected decline in the TFR to continue, these subgroups must be highlighted, understood, and targeted with fertility-and poverty-reducing interventions.