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.
Categories: hep-ph