Molecular crystals consisting of metal-dithiolene complexes have been attracting attention from the viewpoint of the physical property characteristic of the hybrid orbitals composed of p orbitals at ligands and d orbitals at a central metal. This chapter introduces the crystal structures. It describes the details of the 2D structure from the viewpoint of the triangular lattice. The chapter also introduces the diversity in the charge ordered state due to the interchange of the molecular orbital levels. It discusses the electronic transition observed in the reflectance spectra. The chapter describes the methodology for analyzing the electronic state by use of the vibrational spectroscopy. It also describes the vibrational spectra and the electronic state of several X[M(dmit)2]2 salts. The chapter proposes the experimentally obtained parameters classifying the ground states. Various electronic configurations and intermolecular interactions are not always detected by diffraction methods.