Emerging adulthood, viewed through the lens of life course health development, has the potential to be a very positive developmental stage with postindustrial societies giving adolescents and emerging adults a greater opportunity for choice and exploration but also greater challenges with greater educational and social role requirements. The loss of supports and structures offered by schools, families, and child- and family-oriented health and social services means that the emerging adult must rely more on his/her own resources in a less structured environment. This increased agency in the context of less structure is occurring as the human brain is still developing higher-level capacities such as executive functioning. The person-context interactions during EA are many and complex, leading to multiple different pathways through emerging adulthood. Those with sufficient economic and adult supports as well as personal resources and maturity will be more likely to choose well and embark on a positive trajectory during EA. Those lacking these resources, or those with physical and mental health or intellectual disabilities, may struggle during this period and experience a negative trajectory in the spheres of education, vocation, relationships, and health status. The life course health science of EA requires more detailed and deeper analysis of the relationship between family, peers, and societal supports and personal internal resources in order to help promote successful developmental trajectories during EA.