Be/X-ray binaries: An observational approach
  Be/X-ray binaries are the most numerous class of X-ray binaries. They constitute an excellent tracer of star formation and can be used to study several aspects of astrophysics, from mass loss in massive stars to binary evolution. This short review, intended for the non-specialist, presents a summary of their basic observational properties and outlines the physical mechanisms giving rise to these characteristics. 
Ignacio Negueruela (University of Alicante)