Optical reflectivity spectra are investigated on single crystals of La 2- x Sr x CuO 4 over a wide compositional range 0 ≤ x ≤ 0.34 which covers insulating, superconducting and ‘normal’ metallic phases. It is clearly demonstrated that the electronic structure exhibits drastic changes at x ~ 0 and at x ~ 0.25, starting from the x = 0 insulator with a charge-transfer energy gap and approaching a Fermi liquid state for heavy doping.