This chapter provides a general overview on how the ship-propulsor systems work together, and generates a road map for developing the necessary information on propulsor and hull-propulsor interaction. It provides the basic definitions of power and power ratios. The chapter discusses the advantages and disadvantages of propulsors. A major objective of the work of naval architects is to design a hull-propulsor system that accomplishes the transfer with the highest possible efficiency. Most vessels today are driven by marine propeller, water jet propulsion and Voith Schneider propeller (VSP). The most common propulsor is the marine propeller. Water jet propulsion might provide better efficiency as a marine propeller in high speed applications where the propeller is likely to experience significant cavitation. Voith Schneider propellers combine propulsion with steering. VSP can generate thrust in any direction, which gives the vessels their high level of maneuverability.