  This review analyzes the state and advancement of the dark matter halo
concentrations over the last two decades. It begins with presenting the article
that brought the field to the limelight and then follows through with other
research works that studied the concentrations of dark matter haloes over the
ages. Besides the discussion of the halo mass-concentration relation and its
evolution, we examine the effects of cosmology, subhaloes and environment on
the relation. In addition to theoretical halo concentrations, observational
dark matter halo concentrations are also considered. This review synthesizes
the progress in this field into a clear piece of article.
