The fundamental properties of atmospheric aerosols pertinent to atmospheric optics are the size, shape, and refractive index for the entire aerosol population at a given point. Once these properties are established, their interaction with visible radiation can be calculated, and the relevant optical properties can be measured. The most important properties are the concentration and size distribution of particles within the accumulation mode of 0.1 to 1.0mm in diameter. The chemical composition of the aerosol population has a weak influence on optical properties through changing the refractive index, but it is vital for the identification of the origin of the light scattering aerosol. This report reviews the properties of aerosols relevant to their optical behavior. Regulations in these properties suggest that relatively simple parameterizations can be developed which will relate optical properties to aerosol mass. These relationships can then be used with aerosol models to predict visibility and with optical measurements to infer aerosol mass.