Where are the baryons?: hide and seek in the Universe

Most of the baryons in the low redshift Universe appear to be missing.
Hydrodynamic cosmological simulations predict that they reside in the
warm-hot intergalactic medium, WHIM. I will describe recent efforts to
trace the WHIM and determine its physical properties, and discuss the
implications towards the missing baryon problem. I will briefly
outline future missions designed to solve this problem.