The ab-plane optical properties of the high-temperature superconductor Bi2Sr2CaCu2O8 are anisotropic in both the normal and the superconducting state. Consistent with the orthorhombic structure, the principal axes lie along the a and b crystallographic axes, nearly 45 degrees from the Cu-O bond direction. In the normal state, analysis of the temperature-dependent optical conductivity suggests a:scattering rate for the free carriers that shows ab anisotropy in both magnitude and temperature dependence. In;the superconducting state, the anisotropy in the oscillator strength of the superfluid response determined from the far-infrared frequency dependence of sigma(2)(omega) and from a sum-rule analysis leads to a penetration depth lambda(D) that is larger along the b axis than the a axis: (lambda(L)(b)>lambda(L)(a)). [S0163-1829(99)01845-7].