Volume 40 Number 1 March 2009 1 Adolescence and young adulthood have long been rec- ognized as a fluid period in the life span, as individuals move at their own rates through a series of developmen- tal changes and transitional events. In many parts of the world today, that process is taking place on a shifting stage amid social and economic change, where young people are experiencing the transient realities of adoles- cence at many levels, from the intimate context of their families to their exposure through the media to the larger world. In such societies, concomitant changes in youthful sexual behavior are often greeted with considerable con- cern by older generations, especially when accompanied by activities that place adolescents at some risk to them- selves and to their futures. This concern appears to exist in many Asian societies. Appropriate intervention, how- ever, requires an understanding of the means by which these environmental changes and departures from tradi- tional values are related to behavioral change—and it be- gins with an understanding of the changes themselves. This study explores the relationships between these environmental changes and young people’s sexual be- haviors in three Asian settings—three cultures with a heritage of Confucian values—in which broad changes in context and in contact with the outside world have taken place but have occurred in different measure on different timetables. In this first analysis of data from the Three-City Study of Asian Adolescents and Youth: Hanoi, Shanghai, and Taipei, we describe the samples and meth- ods employed and test the project’s basic premise: that clear differences exist across these sites and that, despite these differences, significant variations between adjacent age cohorts within each site can be measured, confirming a hypothesis of ongoing behavioral change. Levels of Change in Adolescent Sexual Behavior in Three Asian Cities Laurie Schwab Zabin, Mark R. Emerson, Li Nan, Lou Chaohua, Gao Ersheng, Nguyen Huu Minh, Yi-Li Chuang, Baai Shyun Hurng, David Bishai, and Robert W. Blum Considerable change in the romantic and sexual behaviors of Asian young people may be occur- ring as traditionally Confucian societies modernize and increase outside contacts. This study explores the dimensions and context of this change in three sites at different stages in the process of modernization: Hanoi (early), Shanghai (intermediate), and Taipei (later stage). A survey was conducted of 17,016 males and females aged 15–24 in urban and rural settings in three large metropolitan areas. Survival analysis and Cox regressions were performed to explore ages of respondents at key transitions and the significance of differences between two age cohorts: 15–19 and 20–24. Significant differences are found in levels of sexual and other transitions, even within the narrow time span reflected by the age cohorts. The findings highlight the differential impact of modernization on adolescent sexual behavior as traditional societies undergo social change, and they underline the importance of context in exploring youthful transitions. (STUDIES IN FAMILY PLANNING 2009; 40[1]: 1–12) Laurie Schwab Zabin is Professor, Robert W. Blum is Professor and Department Chair, David Bishai is Associate Professor, Mark R. Emerson is Research Associate, and Li Nan is a doctoral student, Department of Population, Family and Reproductive Health, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD 21205. E-mail: lzabin@jhsph.edu. Lou Chaohua is Professor and Gao Ersheng is Professor and Director, Shanghai Institute for Planned Parenthood Research. Nguyen Huu Minh is Director, Institute of Family and Gender Studies, Hanoi. Yi-Li Chuang is former Director and Baai Shyun Hurng is Director, Population and Health Research Center, Bureau of Health Promotion, Taiwan. Studies in Family Planning