DDI is definitely one of the largest and most respected players in the global leadership development space. They are a leader global human resources consultancy specializing in leadership development as well as leadership assessments. They help companies transform the way the hire, promote, and develop leaders. Their leadership crosses all levels of leadership including performance and execution, leader selection, leadership development, and succession management. DDI has an impressive list of customers including Siemens, Constellium, Huntington, and VF Corporation.