Exotic hadrons with heavy flavors: X, Y, Z, and related states

both in experiments and in theories. In this review, we provide topical discussions by selecting X, Y, Z particles, to which Belle has made important contributions. These are X(3872), Y (4260), Z(c)(4430)(+), Z(c)(3900)(+), Z(b)(10610)(+), and Z(b)(10650)(+). Based on the current experimental observations, we discuss these states with emphasis on the hadronic molecule whose dynamics is governed by chiral symmetry and heavy-quark symmetry of QCD. We also mention briefly various interpretations and some theoretical predictions for the as yet undiscovered exotic hadrons.