This issue of Optical Engineering offers a series of articles highlighting the reduction-to-practice phase which takes place in the development of an optical system. In this issue, optical hardware evolves from system specification to assembly and test. This evolution follows a pattern that has changed little in the past 364 years, when Gallileo first perfected, then used Hans Lippershey's telescope to discover the satellites of Jupiter. While the pattern remains constant, significant changes have occurred in the development of improved tools and techniques. Science and engineering has provided the lens designer with large computers and faster programs, the optician with better machines and optical materials, and the technician with lasers and other sophisticated test equipment in a concerted effort to advance the state of the optical art. The development and application of this more advanced equipment constantly challenges the experience and training of the applied scientist and optical engineer.