Discusses the determinants of and interrelationships between fertility and four other factors that affect family size--employment, income, length of marriage, and migration. A model is developed characterizing relevant behavior of individual families. Fertility (a process of first reaching a family size goal and then maintaining that level) is analyzed empirically using a formulation based on the model derived from data for the Republic of the Philippines. The goal is related to alternative uses of the wife's time--child rearing or labor force participation--as well as the parents' education. Both employment of the wife and education affect fertility negatively. Population control requires both eliminating unwanted births and reducing the number of desired births. The most cost-effective strategy for curtailing the population growth rate should include not only direct control policies, but also programs not directly aimed at population reduction, such as increased education for the female. 34 pp.