This research explores an important psychological capacity in the current boundaryless career environment—optimism. Optimism is associated with flexibility and adaptability amid stressful situations, which, we argue here may be particularly useful in the current unpredictable career environment. We explore the relationship between optimism and the structure and quality of individuals' developmental networks in a sample of young adults. Analyses are based on a 10-year longitudinal study (1996–2006) of a cohort of 136 individuals who graduated from business school in 1996. Cross-sectional analyses show that the amount of psychosocial support, but not career support, received by individuals is positively associated with optimism. Then, considering the long-term nature of help-giving, longitudinal relational data suggest that the greater one's early-career psychosocial and career support, the greater one's optimism many years hence. In addition, we examined how the rate of change in developmental network support over time is associated with optimism. Findings show that increasing amounts of career and psychosocial support over time were associated with greater optimism later in career. Implications for future research on the boundaryless career, optimism, and developmental relationships are discussed. Copyright © 2010 John Wiley & Sons, Ltd.