An analysis is performed, using the finite element method, of the indentation of a thin elasto-plastic layer resting on or attached to a substrate of a different material, which may also deform plastically. The indentation size, contact pressure, applied load, and amount of plastic deformation are found for the elasto-plastic case, and the results are compared with those found by an elastic analysis. It is found that plastic deformation, which occurs in all indentation tests, has a considerable effect on the results, and that the deformation in the indented layer is also affected by such variables as: the material properties of both layer and substrate, the thickness of the layer, and the condition of the interface between layer and substrate. The “piling-up” that has been observed experimentally in indentation tests is found to depend on the same variables and occurs especially when a thin layer is adhered to a more rigid substrate. The analysis is valid throughout the loading-unloading cycle.