Since 2004 I am a computational cosmologist at the Kavli Institute for Particle Astrophysics and Cosmology and a Professor both at the SLAC National Accelerator Laboratory and the Physics Department at Stanford University. Since August 2013 I am the Director of the Kavli Institute for Particle Astrophysics and Cosmology. I was on the faculty at the Department of Astronomy and Astrophysics at Penn State University in State College Pennsylvania from 2002 until 2004. Before then I was a postdoctoral fellow at the Harvard Smithsonian Center for Astrophysics and at the Institute of Astronomy in Cambridge, UK. My PhD thesis was on the Formation of the First Objects in the Universe which I submitted at the Ludwig-Maxemillian University in Munich in 1999. From 1993 through 1998 I was a visiting scientist at the National Center for Supercomputing Applications at the University of Illinois in Urbana Champaign