The following is a list of the largest optical reflecting telescopes sorted by mirror diameter. Note that two of the first three are not yet operational. This list does not currently include telescopes that are still in the conceptual/proposed stage, such as the Overwhelmingly Large Telescope or the European Extremely Large Telescope; the design stage, such as the Thirty Meter Telescope; or ones still in the early stages of manufacturing such as the Giant Magellan Telescope.