One of the most difficult questions in present-day physics concerns a fundamental theory of space, time, and matter that incorporates a consistent quantum description of gravity. There are various theoretical approaches to such a quantum-gravity theory. Nevertheless, experimental progress is hampered in this research field because many models predict deviations from established physics that are suppressed by some power of the Planck scale, which currently appears to be immeasurably small.

However, tests of Relativity Theory provide one promising avenue to overcome this phenomenological obstacle: many models for underlying physics can accommodate a small breakdown of Lorentz symmetry, and a numerous feasible Lorentz-symmetry tests have Planck reach. Such mild violations of Einstein�s Relativity have therefore become the focus of recent research efforts.

This mini course provides a brief survey of the key ideas in this research field and is geared at both experimentalists and theorists. In particular, several theoretical mechanisms leading to deviations from Relativity Theory are presented; the standard theoretical framework for Relativity violations at currently accessible energy scales (i.e., the SME) is reviewed, and various present and near-future experimental efforts within this field are discussed.