Infrared and far infrared polarized reflectance spectra of β-(BEDT-TTF) 2X (X = I 2Br −, AuI 2 −) are presented. Both have, as in the case of X = I 3 −, the strongest metallic character along the stacking axis, but two-dimensional plasmon behavior is found at low temperatures in all the materials. The distribution of oscillator strength is discussed with special emphasis on the non-Drude features.