Harold Stirling Vanderbilt (July 6, 1884 – July 4, 1970) was an American railroad executive, a champion yachtsman and a champion bridge player and a member of Vanderbilt family.

 He was educated by tutors and at private schools including St. Mark's School, Harvard College (AB 1907), and Harvard Law School, graduating in 1910. He then joined the New York Central Railroad, the centerpiece of his family's vast railway empire, of which his father was president. On his father's death in 1920, Harold inherited a fortune that included the Idle Hour country estate at Oakdale, New York, (on Long Island) and equity in many railway companies.

Following the death of his brother William in 1944, he remained the only active representative of the Vanderbilt family in the New York Central Railroad, serving as a director and member of the executive committee until 1954.

As a boy, Harold Vanderbilt spent part of his summers at the Vanderbilt mansions, the Idle Hour estate in Long Island, New York on the banks of the Connetquot River, Marble House at Newport, Rhode Island, and later at Belcourt (the Newport mansion of his stepfather, Oliver Belmont). As an adult, he pursued his interest in yachting, winning six "King's Cups" and five Astor Cups at regattas between 1922 and 1938. In 1925, he built his own luxurious vacation home at Palm Beach, Florida that he called "El Solano." In addition to being his vacation home, El Solano is also notable for being purchased by former Beatle John Lennon shortly before his murder in 1980.

In 1930, Harold achieved the pinnacle of yacht racing success by defending the America's Cup in the J-class yacht Enterprise. His victory put him on the cover of the September 15, 1930, issue of Time magazine. In 1934 Harold faced a dangerous challenger in Endeavour, as the British boat won the first two races. However, Vanderbilt came back in his yacht Rainbow to win three races in a row and defend the Cup. In 1937 Harold defended the Cup a third time in Ranger, the last of the J-class yachts to defend the Cup. Vanderbilt's wife, Gertrude "Gertie" Lewis Conaway, became the first woman to compete as a team member in an America's Cup yacht race. They were posthumously elected to the America's Cup Hall of Fame in 1993. Later in life Vanderbilt would become Commodore of the New York Yacht Club and would be intricately involved in many successful America's Cup defenses.

In the fall of 1935, Harold began a study of the yacht racing rules with three friends: Philip J. Roosevelt, President of the North American Yacht Racing Union (predecessor to US SAILING); Van Merle-Smith, President of the Yacht Racing Association of Long Island Sound; and Henry H. Anderson. "The four men began by attempting to take the right-of-way rules as they were and amending them. After about six weeks of intensive effort, they finally concluded that they were getting exactly nowhere. It was the basic principles, not the details, that were causing the problems. They would have to start from scratch."

In 1936, Vanderbilt, with assistance from the other three had developed an alternative set of rules, printed them, and mailed a copy to every yachtsman that Harold knew personally or by name in both the United States and England. These were virtually ignored, but a second edition in 1938 was improved, as were following versions. Vanderbilt continued to work with the various committees of the North American Yacht Racing Union until finally in 1960 the International Yacht Racing Union (predecessor to the International Sailing Federation or ISAF) adopted the rules that Vanderbilt and the Americans had developed over the previous quarter century.