Underground Searches for Cold Relics of the Early Universe

We have strong evidence on all cosmic scales, from galaxies to the largest structures ever observed, that there is more matter in the universe than we can see. Galaxies and clusters would fly apart unless they would be held together by material which we call dark, because it does not shine in photons. Although the amount of dark matter and its distribution are fairly well established, we are clueless regarding its composition. Leading candidates are Weakly Interacting Massive Particles (WIMPs), which are 'cold' thermal relics of the Big Bang, ie moving non-relativistically at the time of structure formation. These particles can be detected via their interaction with nuclei in deep-underground, low-background detectors. Experiments dedicated to observe WIMP interactions for the first time reach sensitivities allowing to probe the parameter space predicted by supersymmetric theories of particle physics. Current results of high sensitivity direct detection experiments are discussed and the most promising projects of the future are presented. If a stable new particle exists at the weak scale, it seems likely to expect a discovery within this decade.