How fast and how far China’s fertility declined in the 1990s has long been a matter of considerable debate, despite very low fertility consistently being reported in a number of statistical investigations over time. Most demographers interpreted this as a result of serious underreporting of births in population statistics, due to the family planning program, especially the program strengthening after 1991. Consequently, they suggested that fertility fell only moderately below-replacement level, around 1.8 children per woman from the early 1990s. But some demographers argued that surveys and census may have reflected a real decline of fertility even allowing for some underreporting of births, given the consistency between data sources and over time. They believed that fertility declined substantially in the 1990s, very likely in the range between 1.5 and 1.6 by the year 2000.¶ The controversy over fertility is primarily related to the problem of underreporting of births, in particular the different estimations of the extent of underreporting. However, a correct interpretation of fertility data goes far beyond the pure numbers, which calls for a thorough understanding of different data sources, the programmatic and societal changes that occurred in the 1990s, and their effects on both fertility changes and data collection efforts. This thesis aims to address the question whether the reported far-below-replacement level fertility was a reality of substantial fertility decline or just an illusion arising from underreporting of births. Given the nature of the controversy, it devotes most efforts in assessing data quality, through examining the patterns, causes and extent of underreporting of births in each data source; reconstructing the decline of fertility in the 1990s; and searching corroborating evidence for the decline.¶