There is abundant evidence that leadership development leads to positive impact. But how do we define impact, and what factors should be considered when assessing the results of leadership development? Our comprehensive framework is specifically relevant to leadership development and defines four levels of impact (individual, group, organizational, and societal) as well as three factors that contribute to its effectiveness (leader characteristics, leadership solution, and context). Understanding the four levels will enable organizations to clarify the goals and purpose of their development initiatives and know where to focus measurement. Attending to the contributing factors can help organizations understand the results they are getting and take appropriate steps to maximize the impact of their development initiatives.