A review is provided of ultraviolet (UV) and visible radiative transfer in an atmosphere-sea-ice-ocean system with emphasis on the basic physical principles involved rather than on mathematical/numerical techniques. To illustrate the application of the theory, a few examples are provided. First, we provide a comparison of two different models for radiation penetration into the open ocean, which for a given set of input parameters give identical results. Thus, for a stratified atmosphere-ocean system, our ability to model the transfer of UV radiation and visible light appears to be limited as much by reliable information about the inherent optical properties of marine constituents as by our ability to accurately solve the radiative transfer equation. Second, we discuss a comparison between measured and modeled radiative transfer results in an atmosphere-sea ice-ocean system, which reveals that accurate transmittances as well as accurate values for the radiative energy deposition versus depth can be calculated. Third, we review results of a study showing that multiple scattering in a highly scattering medium such as sea ice gives rise to a marked enhancement of the downward irradiance across the atmosphere-sea ice interface. Finally, we review a recent study in which the modeled radiation field is used to illustrate how the primary production in icy polar waters might be influenced by an ozone depletion. Contrary to previous investigations, this study reveals that a 50% ozone depletion might lead to an increase (∼1%) rather than a decrease in primary productivity.