  We present a brief account of the developments in the description of light
meson resonances using unitarized extensions of the Chiral Perturbation Theory
series, both in energy and temperature. In particular, we describe how these
methods have been recently shown to describe simultaneously the low energy and
resonance regions of meson-meson scattering. This approach could be of
relevance to understand the light scalar mesons since it provides a formalism
that respects chiral symmetry and unitarity and is able to generate resonant
states without any a priori theoretical bias toward their existence,
classification or spectroscopic nature. We will also review how this approach
is also able to describe the thermal evolution of the $\rho$ and $\sigma$
mesons. In addition we review their extensions to higher orders, the most
recent determination of the resonance pole properties, as well as their
behavior in the large $N_c$ limit, which could be of relevance to understand
their spectroscopic nature.
