  Hadrons carrying open heavy flavor, i.e. single charm or bottom quarks, are
among the key diagnostic tools available today for the hot and dense state of
strongly interacting matter which is produced in collisions of heavy atomic
nuclei at ultra-relativistic energies. First systematic heavy-flavor
measurements in nucleus-nucleus collisions and the reference proton-proton
system at Brookhaven National Laboratory's (BNL) Relativistic Heavy Ion
Collider (RHIC) have led to tantalizing results. These studies are now
continued and extended at RHIC and at CERN's Large Hadron Collider (LHC), where
considerably higher collision energies are available. This review focuses on
experimental results on open heavy-flavor observables at RHIC and the LHC
published until July 2012. Yields of heavy-flavor hadrons and their decay
products, their transverse momentum and rapidity distributions, as well as
their azimuthal distributions with respect to the reaction plane in heavy-ion
collisions are investigated. Various theoretical approaches are confronted with
the data and implications for the properties of the hot and dense medium
produced in ultra-relativistic heavy-ion collisions are discussed.
