An ultra-thin reconfigurable absorber concept based on metasurfaces is presented. First, an artificial magnetic conducting (AMC) metasurface absorber is examined that incorporates lumped resistors along with variable lumped capacitors, which allow its frequency response to be tuned. The parasitic effects introduced by the lumped capacitors are compensated by adding resistors whose values are determined using an optimization algorithm known as the covariance matrix adaptation evolutionary strategy (CMA-ES). Second, the feasibility of achieving broadband absorption using frequency selective surfaces (FSSs) comprised of square loops is examined. Such a structure offers greater tunability, and thus wideband absorption can be achieved. First, an absorber that utilizes an FSS comprised by two square loops along with lumped resistors is studied and its wideband absorption properties are demonstrated. Second, an absorber that incorporates a resistive frequency selective surface comprised by four square loops and a center patch is presented.