  The paper gives a short overview of the principles of particle accelerators,
their historical development and the typical performance limitations. After an
introduction to the basic concepts, the main emphasis is to sketch the layout
of modern storage rings and their limitations in energy and machine
performance. Examples of existing machines - among them clearly the LHC at CERN
- demonstrate the basic principles and the technical and physical limits that
we face today in the design and operation of these particle colliders. Pushing
for ever higher beam energies motivates the design of the future collider
studies and beyond that, the development of more efficient acceleration
techniques.
