The contemporary Extension 4-H program is focused on positive youth development, providing experiences that increase the likelihood of enhanced wellbeing and optimal development for 4-H participants. Despite the longevity, reach, and success of the 4-H program, however, with few notable exceptions, there has been relatively little attention paid to elucidating the underlying program theory and the actions that put the theory into motion. As a result, no one model or framework guides the program uniformly across the 4-H system, resulting in numerous ways of describing and measuring the impact of the 4-H program on young people. This paper proposes a 4-H program model that connects the 4-H program context to youth developmental outcomes through the mediating process of youth thriving. The model is based on a synthesis of extensive research conducted in the field of youth development and elucidates the processes that facilitate developmental change in youth. Implications for model use as well as professional development are considered.