The Ulster and Delaware Railroad (U&D) was a railroad located in the state of New York. It was often advertised as "The Only All-Rail Route to the Catskill Mountains." At its greatest extent, the U&D extended 107 miles (172 km) from Kingston Point on the Hudson River through the Catskill Mountains to its western terminus at Oneonta, passing through the counties of Ulster, Delaware, Schoharie and Otsego.

The Catskill Mountains, also known as the Catskills, are a physiographic province and subrange of the larger Appalachian Mountains, located in southeastern New York. As a cultural and geographic region, the Catskills are generally defined as those areas close to or within the borders of the Catskill Park, a 700,000-acre (2,800 km2) forest preserve protected from many forms of development under New York state law.