An overview of the current understanding of the pentaquark baryon
spectroscopy will be given.
After the seminal experimental report on the $\Theta^+$ discovery,
numerous theoretical papers
that attempt to explain its mass and quantum numbers have appeared.
Yet no consensus is given even on its spin nor parity.
The pentaquark spectroscopy is a treasure island for theorists,
who reconsider their quark model picture of the hadrons and
may find a new scheme of hadron spectroscopy.
I will introduce studies based on quark models and on nonperturbative