As medical knowledge and treatments improve, pediatricians' role in promoting children's health continues to change. Genetics and early experiences may have long-term effects on health and development. Theoretical models that influence providers' decisions about the use of health-care resources are: the disease model, the neuromaturational model, the transactional model, and the life course health development model. The authors describe their Life Course Health Development model (LCHD) model and its implications for health-care policy and practice. The LCHD model suggests that a person's health reflects the influence of genetic, biological, behavioral, social, and economic contexts throughout life, with the first 3 years of life being a critical and sensitive time period in development. The LCHD model emphasizes that early experiences, including both risk and protective factors, affect later health.