SIO Reference 64-3. The authors of this report have shared with many colleagues throughout the world in the development of visibility as a science and as an engineering procedure. The report is intended to provide an overview of some applied aspects of this subject. Sufficient input data has been included to enable certain sample visibility calculations to be carried out by those who wish to explore this branch of optical engineering, but a full professional treatment of the subject would require a book-length treatise. In order to achieve broad coverage and yet adequate technical depth in a compact report, it has been deemed best to call upon an integrated team of specialists to produce a unified presentation with each individual contributing in his specialty. Each major section of the present report, therefore, bears the name of the specialist who prepared it.