Each wave is a living entity, a dynamic dance of energy that transforms the ocean’s surface into a playground of endless possibilities. Understanding the principles of this playground is fundamental for surfers, and this begins with the basics of wave theory. This chapter provides a synopsis of the key physics of ocean waves. It will examine the principal wave theories that describe how waves are formed by wind and then disperse across the oceans. Details of the basic principles that underpin all modern wave forecasting systems are discussed. An examination of the records of global wave power is also presented to discuss the state of the marine climate and changes that have occurred as a result of global warming.