Joseph Hennawi is a cosmologist who works at the interface between observations and theory. He often searches for rare objects that serve as unique astrophysical laboratories. This often entails mining the enormous databases produced by modern digital sky surveys. He’s currently mostly focused on studying diffuse gas in the intergalactic and circumgalactic medium using quasar absorption line techniques, and leads the ENIGMA research group at UCSB dedicated to this purpose. Other areas of interest include the nature of dark matter, gravitational lensing, the cosmic microwave background, and the nature of quasars and galaxies at in the early universe.