Investigations have traditionally framed adolescent sexual activity as "problem behavior": socially disapproved behavior that carries acknowledged risks, such as STDs and unintended pregnancy, and may be accompanied by other disapproved behaviors, including substance use and delinquency.¹ This approach has yielded a long list of risk and protective factors in relation to undesired outcomes, but the conceptualization of adolescent sexuality as a problem behavior has also served an important political role. Justifying public investment in the investigation of a sensitive topic like adolescent sexuality is easier when the significance is premised on preventing unintended pregnancy and STDs, as opposed to, for example, the identification of the types of adolescent sexual experiences that enable future sexual health.

However, adolescent sexual behavior is distinct from other problem behavior because its undesirability is primarily a function of age and assumed immaturity, rather than intrinsic and inevitable health risk. Adults interested in improving adolescent health and its implications for adult well-being would not knowingly promote or condone substance use, crime or violence; the negative health implications of those behaviors are clear, regardless of age. On the other hand, presumably most adults desire and would facilitate the achievement of safe, competent and fulfilling sex lives for their children and other youth as they move through the life course. Unfortunately, most of our research does not inform strategies to achieve this goal.

The artificial separation of sexuality between adolescence and adulthood has always been an untenable model, but its inadequacies have become increasingly obvious as behaviors marking the transition to adulthood have changed. The normative sequence of leaving home, finishing one’s education, acquiring a job, marrying and having children has become less common and more nonlinear,² and reversals of markers are frequent (e.g., young adults may return home after completing college). Likewise, changes are evident in the sexual attitudes, norms and behavior of men and women in developed and, increasingly, developing countries.^3,4 Most individuals have sex before marriage,^5,6 rates of marriage have declined and levels of nonmarital cohabitation and births have increased.⁷ These cultural and experiential transformations warrant change in how we conceptualize and study adolescent sexual health and development.

This is not a new idea. There have been numerous calls over many years to shift from an exclusive treatment of adolescent sexuality as problematic to an approach that places commensurate emphasis on positive sexual development and that acknowledges multiple facets of sexuality and sexual health, and their implications for general well-being over the life course.^8–13 Although some relatively recent studies have reflected this direction,^14–17 the focus often remains exclusively on avoiding harm. Furthermore, much of the literature continues to focus on one or two sexual risk behaviors, often examined cross-sectionally, and provides little information about context and the meaning of the behavior to adolescents.¹⁸

If we accept that healthy sexuality is central to general well-being and that healthy adolescence entails active exploration of identity, values, goals and behavior, then our research must include meaningful efforts to identify and understand life-course pathways to sexual well-being. For some adolescents, a fine line may divide exploratory sexual activity that ultimately contributes to positive sexual identity and competence, and sexual activity that significantly increases risk of harm. We do not know how to help youth navigate this line, or even exactly where or what that line is for individuals of diverse physical, psychological and cultural characteristics (e.g., biological sex, physical disability, sexual orientation and gender ideology) who are exposed to varying experiences at different points in the life course.

Therefore, to move the field of adolescent sexual and reproductive health forward, more research must approach sexuality as a developmental process that intersects with other facets of developmental change (e.g., identity, moral development and interpersonal skills) and, like all development, is the product of multiple types or levels of interacting factors (e.g., biological, psychosocial and cultural-contextual factors) that may have bidirectional influences.^19–20 This is a developmental systems approach. A variety of such models have been advanced and are relevant to investigations of sexual development (e.g., ecological,²¹ transactional²² and contextual²³). Life-course theory²⁴ is a natural fit with such approaches, given its conceptualization of development as a trajectory; its emphasis on interactive relationships of biological, behavioral and social-contextual factors; and its focus on how those relationships may be changed by variable timing and sequences of life experiences and transitions. Some efforts to develop systems models of adolescent sexual health²⁵ build on definitions included in existing policy documents.^10,26 For example, the Surgeon General’s Call to Action notes that among other elements, sexual health includes "the ability of individuals to integrate their sexuality into their lives, derive pleasure from it, and to reproduce if they so choose."¹⁰ However, these efforts may not be well known outside of psychology and gender studies, and therefore may not often be used as a springboard for public health or biomedical research in positive sexual development.

In addition to change in perspective and approach, we need to be more inclusive in terms of populations and content studied. The literature has benefited from increasing numbers of methodologically strong investigations of individuals with same-sex interest and sexual behavior; however, other populations, such as individuals with physical, cognitive or emotional disabilities, have been virtually ignored, especially during adolescence. Furthermore, until recently, "sexual behavior" meant coitus. We need to systematically consider more diverse sexual experiences and contexts, how those experiences relate to each other over time, how their subjective meanings change and how the patterns they form ultimately contribute to sexual health. And because sexuality does not make its first appearance at puberty, research into positive sexual development, like studies predicting sexual risk-taking,^27,28 must consider preadolescent factors—not necessarily overtly sexual experiences, but characteristics and life experiences that contribute to sexual health. For example, learning about responsibility and methods of general decision making is relevant to emergent romantic and sexual choices.

Finally, in addition to broadening our perspective, populations and study content, we need to expand and improve methods of studying the development of sexual health. Foremost, developmental analysis requires longitudinal design, especially to test hypotheses about processes that traverse multiple periods of the life course. With some exceptions,^17,29 longitudinal modeling techniques have not been widely applied to sexual behavior. They could be exceptionally useful in examining dynamic aspects of sexuality, such as within-individual variation in indicators of sexual orientation. A second change is to capitalize on the complementary strengths of small- and large-scale longitudinal studies, and thereby facilitate the integration of biological, psychological, behavioral, spatial and contextual data. Small-scale studies typically can explore and refine in-depth, multimethod measurement—for example, the measurement of sexual decisions made in the heat of the moment—that can inform protocols of larger studies. Similarly, studies based on small, relatively homogeneous samples can better determine the generalizability of their findings through related longitudinal work on representative population-based samples.

A systems approach necessitates blending of data types (e.g., biomarkers and personality measures) and of qualitative and quantitative methods, and therefore will often require interdisciplinary collaboration for effective integration. Interdisciplinary research centers or larger "parent projects" that support relevant substudies could examine developmental processes in biological and cultural context, and build theoretical models of life-course sexual health that draw from a variety of perspectives. It may not be possible to achieve full consensus on what constitutes sexual health, either within or across cultures; however, fuller implementation of holistic investigations of sexual development as it plays out in different physical and cultural contexts is necessary to realize the goal of enhancing sexual and reproductive health.