We review the recent theoretical progress of the multiorbital effects on the electron correlations in iron-based superconductors. Studying the metal-to-insulator transitions of the multiorbital Hubbard models for parent compounds of iron-based superconductors, a Mott transition is generally realized. The natures of both the Mott insulating and the metallic phases are affected by the Hund's rule coupling. In alkaline iron selenides, Hund's rule coupling stabilizes a novel orbital-selective Mott phase, in which the iron 3d xy orbital is Mott localized, while other 3d orbitals are still itinerant. We discuss the effects of the orbital selectivity on normal state properties and the superconductivity of the iron-based systems.