Since 1716, when the Province of Massachusetts built Boston Light, scarcely a year has passed that has not seen a new light structure erected somewhere along our sea coasts, on our navigable rivers, or along our lake shores. To tell the story of these lighthouses would be a major undertaking. These stories of some of them, however, have been selected chiefly for their historical interest. Others have been included because their unique locations or types of construction are of more than usual interest. The lighthouse typifies maritime safety. As part of our early coastal defense system, they played a major role in important Coast Guard duties related to military readiness. Additionally, the light’s strategic locations along our coasts aided another early Coast Guard function, law enforcement, by making it possible for cutters to judge their distances from the coast and so prevent smuggling operations within the three-mile limit. The stories of 56 lighthouses have been told here. The stories of hundreds of others, of equal interest, could have been included had space permitted. The oldest lighthouse described is the Boston Light built in 1716. The newest in this booklet is Buzzards Bay Light which is located some five miles off the Massachusetts coast, replacing a lightship that had been there for many years. The distance these lights are visible has been given in the geographical range. The theoretical visibility of a light in clear weather depends upon two factors, the height of the light above water, and its intensity. The height controls what is known as the geographic range, while the intensity controls what is known as the luminous range. As a rule, for the principal lights the luminous range is greater than the geographic, and the distance from which such lights are visible is limited by the earth’s curvature only. Under some atmospheric conditions the glare or loom of these lights, and occasionally the light itself, may be visible far beyond the computed geographic range. On the other hand, and unfortunately more frequently, these distances may be lessened by fog, rain, snow, haze, or smoke. Some of the terms in this booklet may be new to readers. A short glossary of terms follows: _Candlepower_—The luminous intensity of a light expressed in candles. _Lantern_—The glassed-in enclosure on the top of an attended lighthouse which surrounds and protects the lens. Sometimes the entire piece of illuminating apparatus is referred to as the lantern. _Prism_—A device for refracting light. _Radiobeacon_—Electronic apparatus which transmits a radio signal for use in locating a mariner’s position. _Reflector_—An optic which by reflection changes the direction of a beam of light. _Classification of lenses_—Lenses are classified as to size by “order”, the first order being the largest and the sixth order the smallest. The actual size of a lens is expressed by its inside diameter. The following is a list of the standard lenses: