  We review recent advances in the understanding of the Quantum Chromodynamics
(QCD) transition and its nature, paying special attention to the analysis of
chiral symmetry restoration within different approaches based on effective
theories. After presenting some of the main aspects of the current knowledge of
the phase diagram from the theoretical, experimental and lattice sides, we
discuss some recent problems where approaches relying on effective theories
have been particularly useful. In particular, the combination of ideas such as
Chiral Perturbation Theory, unitarity and Ward Identities allows us to describe
successfully several observables of interest. This is particularly relevant for
quantities expected to be dominated by the light meson components of the hadron
gas such as the scalar and topological susceptibilities. In addition, ward
identities and effective Lagrangians provide systematic results regarding
chiral and $U(1)_A$ partner degeneration properties which are of great
importance for the interplay between those two transitions and the nature of
chiral symmetry restoration. Special attention is paid to the connection of
this theoretical framework with lattice simulations.
