The changing landscape that leaders face demands an evolution of leadership development that not only builds skills but also grows a leader's capacity to effectively respond to and manage an ambiguous, uncertain and changing future. Based on adult development theory, we explore the nuanced difference of leadership development through two distinct, but equally useful lenses: horizontal and vertical leadership development. We examined the state of leadership development practice across fifteen large organizations and present differences in how six common leadership development practices including assessments, individual development plans, expert knowledge sharing, mentorship, coaching, and experiential opportunities were used in a more traditional skill-building way, and how principles of vertical development were incorporated. We conclude with specific practical approaches to modify traditional practices to meet emerging needs.