A novel application for frequency selective surfaces (FSSs) is presented. The novel FSS design can harvest power from arbitrarily polarised incident waves. The design does not involve a matching network, which results in a simple, polarisationindependent power harvester. An accurate analytical procedure, to calculate the impedance of the commercially available Schottky rectifiers, is presented. The results are validated by full-wave simulations and by measurements. A simple equivalent circuit model to predict the transmission and reflection characteristics of the gridded-square-loop FSS is employed. The design method is validated for different polarisations and for different incident angles. The addition of lumped elements (R, L, C) in the metallic conductive grid of the FSS is investigated. The waveguide simulator method and full-wave simulations are employed to validate the derived analytical equations. A 3 x 3 and a 5 x 5 RF harvesting FSS have been designed, simulated, fabricated and validated. A radio frequency (RF) to DC conversion efficiency of 25% for the 3 x 3 RF harvester and 15.9% for the 5 x 5 RF harvester is measured at an RF input power level of -6 dBm.