This work presents and analyzes four gaps in public diplomacy (PD) research: between and among disciplines, between theory and practice, between theory and reality, and between theory and technology. The first two are known and have been researched albeit in general connection with foreign policy, not with PD. The other two are just beginning to be researched. PD is the most multidisciplinary field ever developed. Yet, scholars from many disciplines in the humanities, social sciences, and technology haven’t yet found ways to expand collaboration. The world order is moving from a liberal system to an illiberal one. Much of the present literature has been pursued within the liberal order. PD scholars need to explore the roles and functions of PD in the emerging one. AI is relatively new but has already had significant effects on PD. The combination of AI and disinformation could be disastrous to PD. This chapter presents ways to reduce the gaps, but the main conclusion is that only sustained and creative multidisciplinary research can close or reduce these gaps.