The broaad objective of this project is a continuing study of the demographic transition in a developing country, Taiwan, with special attention to fertility and the role of the family planning program. Procedurally, aggregate social changes as well as changes among individuals analyzed, and many data sources and techniques are employed. Specific studies proposed or in progress include: a) Analysis of trends in desired family size, use of contraception, and fertility for couples with different socioeconomic characteristics. b) Attitudinal and behavioral correlates of fertility. c) New scaling techniques to measure sex and number preference for children among couples and analysis of the correlates of desired family size. d) Causes and fertility consequences of changing age at marriage. e) Mathematical models of the reproductive process to study births averted under various birth control regimes. f) Analysis of the long term fertility- contraceptive histories of women who accepted an intra-uterine device early in the family planning program. Data for these studies come from the extensive material available through the Taiwan household registration system, from special sample surveys, and from the records of the family planning program.