The nature of dark matter, observed to date only through its gravitational interactions on galactic and cosmological scales, remains a profound mystery.  In the standard so-called lambda-CDM cosmological model, cold (nonrelativistic) dark matter (CDM)  aggregates through gravity forming a cosmological web as illustrated in the Millennium simulation shown. Visible matter aggregates in gravitationally attractive pools (halos) of dark matter along this web to form galaxies such as the Milky Way and other visible structures. Visible evidence for the gravitational field of dark matter is found in the orbital rates of stars in galaxies and in the gravitational deflection of light (lensing) by galaxies. The key role of dark matter in cosmological history is reflected in the spatial fluctuations in the temperature of matter about 300,000 years after the Big Bang observed in the cosmic microwave background, and in the resulting matter structure distributions.

Relic weakly interacting massive particles (WIMPs) may be a significant dark matter component according to models motivated by cosmological observations and beyond-the-standard-model elementary particle theory. The LUX-ZEPLIN (LZ) xenon WIMP dark matter direct search will scale up proven technology and search for nuclear recoil signals of galactic WIMP interactions. This direct search will complement searches for missing energy events in collider experiments and astrophysical signatures for non-gravitational interactions between dark and standard model matter.