Black holes are at the centre of key issues of modern astrophysics. In their vicinity, matter is found under extreme conditions, and, in addition, they are thought to play a major role in the formation and the evolution of the galaxies. These key objects are ideally studied in the X-Ray and hard X-ray energy range. Indeed, wide band spectra and variability studies in this domain provide unique diagnostics about the black holes environments, as well on the black holes properties themselves. It is moreover believed that a large number of supermassive black holes are obscured, and can be found only in the hard X-ray range.

Tracing the formation and evolution of all supermassive black holes, including the obscured ones, and examining the accretion processes of matter falling into black holes are fundamental topics that will be addressed in priority by the COSPIX mission, which is proposed to ESA in response to the recent call for a Medium-size mission.

In addition, COSPIX will also provide key measurements on the non thermal Universe, particularly in relation to the question of the acceleration of particles, as well as on many other fundamental questions as for example the energetic particle content of clusteres of galaxies.

To reach these goals, COSPIX is proposed as an observatory operating from about 0.1 to more than 100 keV. The payload, carried by two spacecraft in formation flight, features a focusing mission at 30 keV, an angular resolution around 20 arcseconds well beyond any existing or scheduled mission in hard X-rays, and polarimetric capabilities. COSPIX will extensively build-on results obtained these last years in the study of the Simbol-X and IXO missions.

The aim of this workshop is to present and discuss the mission with the community, review its performances in view of the science goals, consolidate the scientific requirements and the science case, and optimize the mission definition in preparation of the proposal due to ESA on December 3rd.

The workshop will essentially be made of invited presentations, although the possibility of having a limited number of contributed presentations focused on ideas to refine the sciene case is envisioned.