Millennium Force is a steel roller coaster located at Cedar Point amusement park in Sandusky, Ohio, United States. Manufactured by Intamin, it was the park's fourteenth roller coaster when it opened in 2000, dating back to the opening of Blue Streak in 1964. Upon completion, Millennium Force broke five world records and was the world's first giga coaster, a term coined by Intamin and Cedar Point to represent a roller coaster that exceeds 300 feet (91 m) in height. It was briefly the tallest and fastest in the world until Steel Dragon 2000 opened later the same year. The ride is also the third-longest roller coaster in North America following The Beast at Kings Island and Fury 325 at Carowinds.

Millennium Force features a 310-foot-tall (94 m) cable lift hill with a 300-foot (91 m) drop, two tunnels, three overbanked turns, and three hills. The coaster also has a top speed of 93 mph (150 km/h). Since its debut, Millennium Force has been voted the number one steel roller coaster ten times in Amusement Today's annual Golden Ticket Awards. Although Millennium Force has been surpassed in height and speed, it remains one of the tallest and fastest coasters in the world.

The planning, design and development phases of Millennium Force took place over four years, from 1996 to 2000. The first rumors that a new record-breaking roller coaster would be built at Cedar Point, which included speculation about a ten-inversion roller coaster from Bolliger & Mabillard and an Arrow Dynamics MegaLooper, began circulating in early 1998. A roller coaster from D. H. Morgan Manufacturing was also rumored. On July 2, 1999, Cedar Fair Entertainment Company filed a trademark for the name Millennium Force, which raised more speculation about what the ride would be like. About a week later, the first track pieces were seen at the park, and it was confirmed that the ride would be manufactured by Intamin. Cedar Point officials also confirmed that it would not have inversions.

Millennium Force was announced on July 22, 1999. It would be the tallest roller coaster in the world, taking the record from Fujiyama at Fuji-Q Highland in Japan. The ride cost $25 million to design and build. Cedar Point, Intamin, and Werner Stengel designed the layout of the ride. After the ride was announced, several disputes about whether Millennium Force or Superman: The Escape was the tallest and fastest roller coaster in the world arose between Cedar Point and Six Flags Magic Mountain. Superman: The Escape is 415 feet (126 m) high and its speed is 100 miles per hour (160 km/h); however, it is a shuttle roller coaster, not a complete-circuit roller coaster.

Construction started in August 1999 when the site was cleared. Millennium Force was built in the Frontier Trail section of the park. The ride involved the relocation of the Giant Wheel and the Cedar Point and Lake Erie Railroad. The removal and relocation of the Giant Wheel began in October on closing day; the first of 226 supports was installed on October 11, starting at the brake run. Two hundred twenty-six footers, each about 5 feet (1.5 m) deep were dug; the largest ones were 56 by 56 feet (17 by 17 m). The concrete construction was done by Mosser Construction. The lift hill was topped off in early January 2000.

The ride's construction took seven months, and 120 construction workers and project managers participated. Testing took two months. The park conducted a "pull-through" by pulling a train along the course to ensure proper clearance. The ride was inspected and tested with water-dummies on the trains.

The first media event was held on May 11, 2000, and the ride opened to the public two days later on May 13. When it opened, it broke six world records. It was the first Giga Coaster and was the world's fastest complete-circuit roller coaster, but was later overtaken by other rides. The ride was so popular that guests consistently waited three to four hours to board. About a month after Millennium's debut, Cedar Point introduced a virtual queue system, "Ticket to Ride", which allowed visitors to buy a ticket then return later and wait in a shorter line. In August, Cedar Point engaged John Hancock and Associates and Stalker Radar of Indianapolis to measure the height and speed of Millennium Force. The height was measured at 310 feet 11 inches (94.77 m), and the speed was measured at 93 miles per hour (150 km/h), slightly faster than what the park had been advertising (92 mph (148 km/h)).

Before the start of the 2004 season, Millennium Force's seat belts were modified because of an incident that occurred on Superman the Ride, a similar roller coaster at Six Flags New England. The new seat belts were shorter and some riders had difficulties with them. Audio played during the ascent up the cable lift hill, but it is believed to have been removed sometime between 2004-2010. While it is rumored that other audio may have been featured in the past, it is unknown. The roller coaster's layout was repainted over a three-year period, before the 2011, 2012 and 2013 seasons. In 2012, the park added a new LED lighting system.