  Observations in the optical, in X-rays, and gravitational lensing of
galaxies, clusters of galaxies, and large-scale structure are beginning to
provide clues to the dark matter problem. I review the impact of these
observations on some of the main questions relating to dark matter: How much
dark matter is there? Where is it located? What is the nature of the dark
matter? and what is the amount of baryonic dark matter.
