The chapter outlines a range of materials and techniques that can be employed to improve sunlight capture for application in photovoltaics (PV). We review processes such as simple luminescence down-shifting structures, luminescent (or fluorescent) solar collectors and light trapping via a frequency shift which result in an increase of the solar photon flux and significant reduction in PV material requirements. A simple two-flux model is presented within a unified treatment for the collectors and down-shifting structures to estimate re-absorption losses and to determine the collection efficiency based on spectroscopic measurements of the absorption and luminescence spectra. Photon frequency management materials are reviewed which use efficient resonance energy transfer to wavelength shift the incoming solar flux. We show that frequency photon management represents a powerful tool, allowing enhancement in light trapping above the Yablononovitch limit and leading to potentially highly efficient, but employing very thin crystalline silicon, solar cells.