The interaction of high-pressure waterjets with fluids and solids is characterized by the possibility to apply determined stresses with a defined quantity of energy. Beside its classical application in the material and surface processing, the high-pressure waterjet technique found entry into the comminution technique, particularly in connection with new tasks in the environmental and recycling industry. In this contribution, fundamentals and mechanisms of high-pressure waterjets as well as their interactions with solids will be presented. Examples of the use of high-pressure waterjets for comminution are given. (C) 2004 Elsevier B.V All rights reserved.