The Fort Harrison Hotel has served as the main building of the Church of Scientology's campus in Clearwater, Florida, called the Flag Land Base, since 1975. It is owned and operated by the Flag Service Organization. The hotel has 11 stories, 220 rooms, three restaurants, a swimming pool, and a ballroom. The building is connected by a skywalk to the Flag Building.

The hotel opened in 1926 as the "New Fort Harrison Hotel", replacing the former Fort Harrison Hotel. It was built by developer Ed Haley and was used as a community center for many years. The hotel was operated by Ransom E. Olds, inventor of the Oldsmobile, from 1926 until his death in 1950.

The name comes from Fort Harrison, a Seminole War-era U.S. Army fort built in the 1830s, south of today's downtown Clearwater. The fort was named for William Henry Harrison and was the western counterpart of Fort Brooke in what became Tampa. (See also the history of Clearwater.)

In 1953, the hotel was bought by the Jack Tar Hotels and became known as the "New Fort Harrison Hotel, a Jack Tar Hotel". The company added a cabana to the pool area.

By the 1970s, the hotel began to fall into disrepair. On October 27, 1975, the Church of Scientology, as part of its plan to take over Clearwater, purchased the building under the names "Southern Land Development and Leasing Corp" and "United Churches of Florida Inc" for $2.3 million cash. In 1976, the Church of Scientology's connection and the named purchasers was reported by the St. Petersburg Times, as was the Church's plan for a $2.8 million restoration and upgrade of the hotel.

In 2007, the Church announced that the hotel would undergo another $20 million restoration project, which was completed in 2009 at a reported cost of $40 million.

In 2024, the Pinellas County Property Appraiser estimated the market value of the property at $28 million.

In 1989, the Church of Scientology said the Fort Harrison Hotel was used to feed, train and house visiting practitioners. From its initial purchase, the hotel has been used for numerous functions by the Church of Scientology including staff housing, offices, restaurants, conference rooms, classrooms, a ballroom, and as a hotel for visiting practitioners. Over the years, as Scientology has expanded their real estate holdings in Clearwater, several functions have been moved to other buildings. In 2013 they opened the newly-constructed Flag Building across the street, to which they built a skyway across Ft. Harrison Avenue.