  We discuss how future X-ray instruments which are under development can
contribute to our understanding of the non-thermal Universe. Much progress has
been made in the field of X-ray Astronomy recently, thanks to the operation of
modern X-ray telescopes such as Chandra, XMM-Newton, Suzaku, and Swift, but
more in-depth investigation awaits future missions. These future missions
include ASTROSAT, NuStar, e-ROSITA, ASTRO-H and GEMS, which will be realized in
the next decade, and also much larger projects such as Athena and LOFT, which
have been proposed for the 2020's. All of those are expected to bring a variety
of novel observational results regarding astrophysical sources of high-energy
particles and radiation, i.e. supernova remnants, neutron stars, stellar-mass
black holes, active galaxies, and clusters of galaxies among others. The
operation of the future X-ray instruments will proceed in parallel with the
operation of Fermi-LAT and the Cherenkov Telescope Array. We emphasize that the
synergy between the X-ray and gamma-ray observations is particularly important,
and that the planned X-ray missions, when in conjunction with the modern
gamma-ray observatories, will indeed provide a qualitatively better insight
into the high-energy Universe.
