The dielectric functions and optical constants of various metals, which have been incorporated into solar cell devices as front and rear electrodes, are summarized. The metals described here include the group-Ib (Cu, Ag, Au), IIa (Mg), IIIb (Al), IVa (Ti), VIa (Cr, Mo, W), and VIII (Ni, Pt) metals. The optical constants of C (graphite), which has been applied widely for CdTe solar cells, are also shown. It is established in this chapter that the metal dielectric functions in the whole near-infrared/visible/ultraviolet region (1–5 eV) can be parameterized almost perfectly by the combined use of the Tauc-Lorentz and Drude models. For the modeling with the Tauc-Lorentz model, several transition peaks are assumed in the analyzed region. In this chapter, the parameterization results for all the metals are summarized, together with the tabulated optical constants. The dielectric function and optical constants of various metals are also compared. Moreover, the reflectances at semiconductor/metal interfaces in crystalline Si, Cu(In,Ga)Se2 and hybrid perovskite [HC(NH2)2PbI3] solar cells are calculated and their results are discussed.