  Since the discovery of the first charmed meson in 1976, many open-charm and
open-bottom hadrons were observed. In 2003 two narrow charm-strange states
$D_{s0}^*(2317)$ and $D_{s1}(2460)$ were discovered by the BaBar and CLEO
Collaborations, respectively. After that, more excited heavy hadrons were
reported. In this work, we review the experimental and theoretical progress in
this field.
