X-ray observations of active galactic nuclei and black-hole binaries
offer a unique laboratory for testing general relativity in the
strong-gravity regime, for studying accretion physics around black
holes, and for constraining properties of accreting black holes. This
book represents the author's Doctoral Thesis. It contains a brief
introduction to the black-hole physics and X-ray astronomy as well as
the original scientific results. A special attention is focused on black
hole spin measurements employing the relativistic iron line profiles in
the X-ray domain.