Preference theory is a new approach to explaining current and future patterns of employment and fertility among women in modern societies. Although economists usually claim that preferences cannot be measured, methods for identifying women's and men's lifestyle preferences were developed and applied in British (and Spanish) national surveys, confirming the results of previous British and American studies showing three distinct lifestyle preference groups. The results confirm the heterogeneity of women's preferences and suggest that preferences are the primary determinant of fertility and employment decisions. The implications for policies to raise fertility are discussed.