  We review the properties and nature of luminous high-redshift radio galaxies
(HzRGs, z > 2) and the environments in which they are located. HzRGs have
several distinct constituents which interact with each other - relativistic
plasma, gas in various forms, dust, stars and an active galactic nucleus (AGN).
These building blocks provide unique diagnostics about conditions in the early
Universe. We discuss the properties of each constituent. Evidence is presented
that HzRGs are massive forming galaxies and the progenitors of brightest
cluster galaxies in the local Universe. HzRGs are located in overdense regions
in the early Universe and are frequently surrounded by protoclusters. We review
the properties and nature of these radio-selected protoclusters. Finally we
consider the potential for future progress in the field during the next few
decades. A compendium of known HzRGs is given in an appendix.
