<p>Over past decade, there has been increased use of results-based management in Vietnam and other countries, but little empirical research exists on results-based planning (RBP) in the planning functions of public organizations. Some experiences suggest that managerial leadership may be among the determinants of success, affecting whether and how RBP is used. This thesis answers the following question: What is the impact of leadership styles by public managers on the practices of RBP? Using empirical observations of current RBP in Vietnamese public organizations and a multiphase mixed method design, this study finds that transformational, transactional, and autocratic leadership styles are often concurrent among public managers (but in varying intensities), and these ‘combined’ leadership styles have a direct, positive, and strong effect on the use and outcomes of RBP practices. This study also finds that leadership effects on RBP are stronger than other organizational factors examined (RBP-related training, bureaucratic culture, funding). Furthermore, among three components of these combined leadership styles, transformational leadership has the greatest contribution to the higher performance of RBP practices. The findings of this research also show the specific leadership behaviors by public managers that are most associated with the increased RBP. This study contributes to the literature by offering empirical evidence of the role of leadership in deploying reforms such as results-based planning in a context of a developing country. It also provides public organizations with knowledge of leadership styles for implementing such reforms.</p>