Survey investigations, with the end goal of monitoring the entire celestial sphere, have become a priority in astronomy. This book is the first monograph devoted to wide-field telescopes, intended to bridge the gap between astronomers and professional opticians. It emphasizes the deep connection between classical and new telescopes, as well as the continuity of ideas underlying the development of telescope construction. The contents are presented in the simplest form to promote a clear understanding of new designs; descriptions of optical systems are accompanied by extensive graphic information provided by Zemax. Both exact modern optimization and the theory of aberrations are used in explanations, with the former given priority.