Fear Street Part Three: 1666 (titled onscreen as Fear Street 1666 for its first half and Fear Street 1994: Part 2 for its second half) is a 2021 American supernatural period horror film directed by Leigh Janiak, who co-wrote the screenplay with Phil Graziadei and Kate Trefry. Based on the book series of the same name by R. L. Stine, it is the third and final installment of the Fear Street trilogy after Part One: 1994 and Part Two: 1978, and stars Kiana Madeira, Ashley Zukerman, Gillian Jacobs, Olivia Scott Welch, Benjamin Flores Jr., and Darrell Britt-Gibson. The film follows the origins of Shadyside's curse in the mid-17th century and the survivors in 1994 who try to put an end to it.

Produced by Chernin Entertainment, a film adaptation of Fear Street began development at 20th Century Fox in 2015, with Janiak hired in 2017. Filming for the trilogy took place back-to-back from March to September 2019 in Georgia, with the intention of a theatrical release in June 2020. However, due to the COVID-19 pandemic and the acquisition of 21st Century Fox by Disney, Chernin Entertainment ended their distribution deal with 20th Century Studios and sold rights to Netflix in August 2020.

Fear Street Part Three: 1666 premiered at the Los Angeles State Historic Park on July 14, 2021 and was released by Netflix on July 16, 2021. It received generally positive reviews from critics, who described the film as an effective conclusion to the trilogy.