This 2nd edition lays out an updated version of the general theory of light propagation and imaging through Earth’s turbulent atmosphere initially developed in the late ‘70s and ‘80s, with additional applications in the areas of laser communications and high-energy laser beam propagation. New material includes a chapter providing a comprehensive mathematical tool set for precisely characterizing image formation with the anticipated Extremely Large Telescopes (ELTS), enabling a staggering range of star image shapes and sizes; existing chapters rewritten or modified so as to supplement the mathematics with clearer physical insight through written and graphical means; a history of the development of present-day understanding of light propagation and imaging through the atmosphere as represented by the general theory described. Beginning with the rudimentary, geometrical-optics based understanding of a century ago, it describes advances made in the 1960s, including the developmentof the ‘Kolmogorov theory,’ the deficiencies of which undermined its credibility, but not before it had done enormous damage, such as construction of a generation of underperforming ‘light bucket’ telescopes. The general theory requires no a priori turbulence assumptions. Instead, it provides means for calculating the turbulence properties directly from readily-measurable properties of star images. This 2nd edition lays out an updated version of the general theory of light propagation and imaging through Earth’s turbulent atmosphere initially developed in the late ‘70s and ‘80s, with additional applications in the areas of laser communications and high-energy laser beam propagation. New material includes a chapter providing a comprehensive mathematical tool set for precisely characterizing image formation with the anticipated Extremely Large Telescopes (ELTS), enabling a staggering range of star image shapes and sizes; existing chapters rewritten or modified so as to supplement the mathematics with clearer physical insight through written and graphical means; a history of the development of present-day understanding of light propagation and imaging through the atmosphere as represented by the general theory described. Beginning with the rudimentary, geometrical-optics based understanding of a century ago, it describes advances made in the 1960s, including the development ofthe ‘Kolmogorov theory,’ the deficiencies of which undermined its credibility, but not before it had done enormous damage, such as construction of a generation of underperforming ‘light bucket’ telescopes. The general theory requires no a priori turbulence assumptions. Instead, it provides means for calculating the turbulence properties directly from readily-measurable properties of star images. T. Stewart McKechnie, BS (Hons), MS, PhD, studied at Edinburgh University and Imperial College London, where he subsequently undertook postdoctoral research and lectured in Optics. After working at Loughborough University (UK), Dr. McKechnie went on to become a Consultant in Optics and program leader for optical system development of light valve and CRT-based projection TV systems at North American Philips Laboratories. In 1988 he joined Martin Marietta Corporation, Albuquerque, and in 1989 transferred to Lentec Corporation, where he was responsible for optics support at the Developmental Optics Facility relating to development of optical components for HEL systems. From 1992 to 2003 Dr. McKechnie was an Independent Optics Consultant at McKechnie Optics Research, his clients/projects including ITT Corp, NASA, the ATP Testbed program (formerly HABE), S Systems Corp, Aerotherm Corporation, Imaging Systems Laboratory (Florida Atlantic University) and Sandia National Laboratories. Between2003 and 2009 he worked at ITT Corporation, Advanced Engineering & Sciences, Albuquerque, New Mexico, as Chief Scientist with responsibility for optical design, modeling, and construction of Light Detection and Ranging (LIDAR) and Laser Detection and Ranging (LADAR) remote sensing systems.