  X-ray polarimetry promises to give qualitatively new information about
high-energy sources. Examples of interesting source classes are binary black
hole systems, rotation and accretion powered neutron stars, Microquasars,
Active Galactic Nuclei and Gamma-Ray Bursts. Furthermore, X-ray polarimetry
affords the possibility for testing fundamental physics, e.g. to observe
signatures of light bending in the strong gravitational field of a black hole,
to detect third order Quantum Electrodynamic effects in the magnetosphere of
Magnetars, and to perform sensitive tests of Lorentz Invariance. In this paper
we discuss scientific drivers of hard (>10 keV) X-ray polarimetry emphasizing
how observations in the hard band can complement observations at lower energies
(0.1 - 10 keV). Subsequently, we describe four different technical realizations
of hard X-ray polarimeters suitable for small to medium sized space borne
missions, and study their performance in the signal-dominated case based on
Monte Carlo simulations. We end with confronting the instrument requirements
for accomplishing the science goals with the capabilities of the four
polarimeters.
