  Exotic multi-quark states are examined in the quark model and in QCD. Current
status of theoretical studies of the pentaquark Theta^+ is reported. We show
recent analyses of multi-quark components of baryons. A novel method to extract
a compact excited state in the lattice QCD is applied. We also discuss how to
determine mixings of different Fock components in the hadron in the QCD sum
rule approach.
