||Identifying low energy degrees of freedom and their interplay in correlated electron materials is a key to the understanding of their physical properties. For the metal-to-insulator-transitions (MIT) in particular, the strong electronic correlation plays a crucial role in the charge localization of the systems by an intricate interrelationship of lattice, charge, orbital, and spin degrees of freedom. In this talk, I will discuss the origin of the recently reported MIT in hydrogenated HxVO2, showing insulator to metal transition as increasing H doping and reentrance to the insulating phase in the fully hydrogenated limit (x=1). We investigate the change in optical conductivity as increasing H content by spectroscopic ellipsometry, showing a gap opening with a structural transition as approaching fully hydrogenated limit. The insulating phase of fully hydrogenated HVO2 is investigated using density functional plus dynamical mean-field theory (DFT+DMFT). We identify the paramagnetic insulating phase in which both the dimer-induced bonding-antibonding splitting and the Mott-gap opening with orbital ordering stabilized by electron correlations play an important role in the MIT. We find that the calculated optical conductivity is in good agreement with experimental data and that the orbital structure from DFT+DMFT solution is consistent with X-ray linear dichorism and polarization dependent optical conductivity, supporting the orbital dependent Peierls and Mott insulating phase of HVO2.