The signal from a confocal measurement as the focal volume is scanned down into a tissue yields an exponential deeay versus depth (z_rbeus), signal = rho exp(-mu z_focus), where rho [dimcnsionless] is the local reflectivity and mu [I/cm] is an attenuation coefficient, A simple theory for how rho and mu depend on the optical properties of scattering (mu_s) and anisotropy (g) is presented. Experimental measurements on 5 tissue types from mice (white and gray matter of brain, skin, liver, muscle) as well as 0.1-μm-dia. polystyrene microspheres are presented. The tissues have similar mu_s values (about 500 [I/cm]) but variable g values (0.8-0.99). Anisotropy appears to be the primary mechanism of contrast for confocal measurements such as reflectance-mode confocal scanning laser microscopy (rCLSM) and optical coherence tomography (OCT). While fluorescence imaging depends on fluorophores, and absorption imaging depends on chromophores, the results of this study suggest that contrast of confocal imaging of biological tissues depends primarily on anisotropy.