Over the last four hundred years, since Galileo first used a small refractive telescope to study the Cosmos, the development of observational astronomy has been a technology-driven field as astronomers have constantly struggled to build ever-larger telescopes. The fundamental limit to the power of a telescope has always been the aperture, or collecting area of the primary optic, initially a refracting lens, which today is the primary mirror. The drive to build ever-larger telescopes is motivated by the need to collect as much light as possible and, thereby, increase the signal-to-noise (S/N) ratio of observations. In addition, a larger ground based telescope with adaptive optics has increasingly better angular resolution as the diameter of the primary mirror increases. In 1977, Jerry Nelson of the University of California Observatories, Lick Observatory realized the impractically of enlarging the monolithic glass reflector of the Hale Telescope, due to unmanageable increases in the expense of construction as well as the thickness, weight, and risk of fracture of the glass. A key decision was made: a design path would be pursued that could lead to an entire new generation of telescopes, not just a single giant telescope. It was realized that the centuries-old telescope construction paradigm for monolithic telescopes could be supplanted by using modern electrical sensors and electronic servo-controls to build optical quality mirror surfaces of any conceivable size from an array of many small (∼1 m scale) and thin hexagonal segments. © 2015, Elsevier Ltd. All rights reserved.