This thesis examines the splashing of water drops on a water surface and the entrainment of air by a jet plunging into a liquid pool. Both these phenomena have been examined photographically and as a result mechanisms have been proposed for them both. Models based on these suggested mechanisms have been tested against experimental data. Measurements have been taken of air entrainment rates and a correlation suggested relating this to the properties of the jet. The model of the air entrainment rate as a function of jet roughness has been confirmed and another proposed for the rate of air entrainment as a function of bubble penetration depth into the pool.