A roller coaster is a type of amusement ride employing a form of elevated railroad track that carries passengers on a train through tight turns, steep slopes, and other elements. Roller coasters are usually designed to produce a thrilling experience, though some roller coasters aim to provide a more gentle experience. Trains consist of open cars connected in a single line, and tracks are typically built and designed as a complete circuit in which trains depart from and return to the same loading station. One notable exception is Racer at Kennywood, West Mifflin, PA, which has the train return to the opposite loading track due to its unique Möbius design. The rides are typically found in amusement parks around the world but can be located in shopping malls, and zoos. . The Roller Coaster DataBase estimates there are approximately 6,000 extant roller coasters as of October 2025^[update].

The earliest progenitors to the modern roller coasters were the "Russian Mountains", which first appeared in the 17th century. LaMarcus Adna Thompson obtained one of the first known patents for a track-based roller coaster design in 1885, based on the Switchback Railway which opened a year earlier at Coney Island. Today, most roller coasters are built out of steel, which can allow for more intense forces and inversions (where the rider is upside down).

The oldest roller coasters are believed to have originated from the so-called "Russian Mountains"; specially constructed hills of ice located in the area that is now Saint Petersburg, Russia. Built in the 17th century, the slides were built to a height of between 70 and 80 feet (21 and 24 m), had a 50-degree drop, and were reinforced by wooden supports. Later, in 1784, Catherine the Great is said to have constructed a sledding hill in the gardens of her palace at Oranienbaum in St. Petersburg.

The Riding Mountain (aka La Grande Glisade) entertainment pavilion designed by Bartolomeo Francesco Rastrelli for Tsarskoye Selo royal residence was built in 1754–1757. In Russian it was known as Katalnaya gora (Катальная гора, literally "Mountain for riding") It was a huge building in the shape of rotunda. It had a trail with five hills, which could be covered with ice in winter. In the summertime, the trails used trolleys on wheels secured in the steel grooves mounted on the wooden trails. Due to a pendulum-like motion based on inertia, all five hills could be traversed in one ride. The ride was engineered by Russian scientist Andrey Nartov. Katalnaya gora was dismantled in 1792–1795. Currently in its place is the Granite Terrace in the Catherine Park.

Two early forms of roller coaster were built in France in 1817. Les Montagnes de Belleville (Les Montagnes Russes à Belleville) in Belleville, Paris had wheels attached to carriages and locked on tracks. The Promenades Aériennes, opened in Parc Beaujon in Paris on July 8, 1817 had wheeled cars securely locked to the track, guide rails to keep them on course, and higher speeds. It spawned half a dozen imitators, but their popularity soon declined.

However, during the Belle Epoque they returned to fashion. In 1887, Catalan entrepreneur Joseph Oller, co-founder of the Moulin Rouge music hall, constructed the Montagnes Russes de Belleville, "Russian Mountains of Belleville" with 656 feet (200 m) of track laid out in a double-eight, later enlarged to four figure-eight-shaped loops.

In 1827, a mining company in Summit Hill, Pennsylvania constructed the Mauch Chunk Switchback Railway, a downhill gravity railroad used to deliver coal to Mauch Chunk, Pennsylvania – now known as Jim Thorpe. By the 1850s, the "Gravity Road" (as it became known) was selling rides to thrill seekers. Railway companies used similar tracks to provide amusement on days when ridership was low.

Using this idea as a basis, LaMarcus Adna Thompson began work on a gravity Switchback Railway that opened in 1884 at Coney Island in Brooklyn, New York. Passengers climbed to the top of a platform and rode a bench-like car down the 600-foot (183 m) track up to the top of another tower where the vehicle was switched to a return track and the passengers took the return trip. This track design was soon replaced with an oval complete circuit. In 1885, Phillip Hinkle introduced the first full-circuit coaster with a lift hill, the Gravity Pleasure Road, which became the most popular attraction at Coney Island. Not to be outdone, in 1886 Thompson patented his design of roller coaster that included dark tunnels with painted scenery. "Scenic railways" were soon found in amusement parks across the county.