  Firstly, I give a brief summary of the current understanding of QCD below and
near $T_c$ (the critical temperature of the chiral transition). Some emphases
are put on the qualitative difference between the Yukawa regime ($T \sim 0)$
and the Hagedorn regime ($T \sim T_c$). Secondly, the dynamical phenomena
associated with the chiral transition, in particular, the spectral changes of
hadrons in hot and/or dense medium are reviewed from the point of view of the
QCD spectral sum rules. Confusions on the QCD sum rules at finite
temperature/density are also clarified and remarks on the effective lagrangian
approaches are given. Thirdly, planned experiments to detect the spectral
changes in medium are summarized.
