Formation of the First Black Holes: Current observational status
  In this chapter, we review the current observational status of the first
supermassive black holes. It is clear that such a review can hardly be
complete, due to the wealth of surveys that has been pursued, including
different wavelengths and different observational techniques. This chapter will
focus on the main results that have been obtained, considering the detections
of z~6 supermassive black holes in large surveys such as SDSS, CFHQS and
Pan-STARRS. In addition, we will discuss upper limits and constraints on the
population of the first black holes that can be derived from observational
data, in particular in the X-ray regime, as these provide additional relevant
information for the comparison with formation scenarios.
