Abstract: Methods and apparatus for chemical mechanical polishing of substrates, such as semiconductor wafers, which employ retaining rings to hold a substrate in place during the polishing process. The retaining rings have surface characteristics that may be used to improve polishing uniformity, especially at a wafer periphery, and/or to improve removal rate of a chemical mechanical polishing (“CMP”) system. The surface characteristics may be recesses and/or protrusions on the pad-facing surface of a CMP retaining ring, which during polishing contact and act to flatten a CMP polishing pad beneath the substrate. Near the edge the surface characteristics may also condition the surface of a polishing pad during polishing and may be further configured to improve slurry transport.