  The existence of dark matter as evidenced by numerous indirect observations
is one of the most important indications that there must be physics beyond the
Standard Model of particle physics. This article reviews the concepts of direct
detection of dark matter in the form of Weakly Interacting Massive Particles
(WIMPs) in ultra-sensitive detectors located in underground laboratories,
discusses the expected signatures, detector concepts, and how the stringent
low-background requirements are achieved. Finally, it summarizes the current
status of the field and provides an outlook on the years to come.
