Offshore wind turbines are always subjected to highly varying aerodynamic and hydrodynamic loads which dictate the design phase of the wind turbine substructures. The breaking wave forces yield the highest hydrodynamic loads on substructures in shallow water, particularly plunging breaking waves. Due to the complex and transient nature of the impact forces, the description requires more details concerning the physical properties of breaking waves and the response of the structure. The objective of this paper is to give an overview of the previous and recent research on wave impact forces and the key issues pertaining to these forces on offshore wind turbine substructures.