  Astrophysical observations indicate that about 23% of the energy density of
the universe is in the form of non-baryonic particles beyond the standard model
of particle physics. One exciting and well motivated candidate is the lightest
supersymmetric partner particle (LSP), which could be a weakly interacting
massive particle (WIMP) left over from the Big Bang. To determine that the LSP
is the dark matter, it is necessary both to measure the particle's properties
at an accelerator and to detect the particle in the galaxy directly (or
indirectly). Direct detection of these particles requires sophisticated
detectors to defeat much higher-rate backgrounds due to radioactivity and other
sources. Promising techniques identify individual interactions in shielded
fiducial volumes and distinguish nuclear-recoil signal events from
electron-recoil backgrounds, based on the timing, energy density, and/or the
division of the energy into signals of ionization, scintillation, or phonons. I
review the techniques of the dozens of experiments searching for WIMPs and
summarize the most interesting results and prospects for detection.
