Marine propulsors are key components of the many thousands of ships and boats operating in oceans, lakes, and rivers around the world. The performance of propulsors are important for the environmental impact of ships, underwater noise impact on aquatic fauna, and crew and passenger comfort and safety. This book presents nineteen papers devoted to the hydrodynamics of different types of marine propulsors (conventional propellers, thrusters, and novel solutions). Most of the papers are extended papers from the sixth International Symposium on Marine Propulsors (SMP 2019). Several of the papers deal with cavitation, vortices, and energy saving devices. The papers present high-quality research performed using Computational Fluid Dynamics (CFD) and Experimental Fluid Dynamics (EFD) as well Artificial Intelligence (AI).