Astronomers infer that the universe contains huge amounts of a mysterious, invisible substance called "dark matter". To account for the structure of galaxies and clusters of galaxies, the universe must contain six times more dark matter than ordinary atomic matter. We do not know what this stuff is made of. It should be composed of particles of some kind, and, if so, we should be able to see those particles streaming in from space. However, the particles must be very weakly interacting, so exotic methods are needed to make them visible. In this lecture, Sunil will present the evidence for dark matter. He will then describe some of the technologies that are now being used to search for dark matter particles. Among these, Sunil will present his own search experiment, one of the world's most sensitive, which uses ultra-pure crystals maintained at cryogenic temperatures in a deep underground laboratory.