The pace of fertility decline in sub-Saharan Africa will be the single most important factor in whether the global population reaches the UN’s high projection of nearly 11 billion in 2050, or remains closer to the low projection of 8 billion. In recent years, the high projection has seemed more likely, as sub-Saharan Africa has been marked by stalled fertility declines and stagnant rates of contraceptive use. Survey results released over the past year showing dramatic increases in contraceptive use in Ethiopia, Malawi, and Rwanda therefore set demographers and the family planning community abuzz, signaling that concerted efforts to improve health services had paid off and fertility rates were on the decline. But in recent months, additional surveys from Mozambique, Uganda, and Zimbabwe have shown that those positive trends are not universal.