Accelerators for the 21st century

Accelerators for the 21st century at the high energy frontier will all be colliding beam devices. Three types of colliders are discussed, linear e + e- colliders muon colliders, and hadron colliders. In all three cases, typical values of the most relevant parameters are presented, the state of component development is discussed, schedules for the earliest dates of construction are shown, and critical issues needing R&D are mentioned. However, low-energy accelerators, synchrotron light sources, etc. are not discussed at all.