This Is Spinal Tap (also known as This Is Spın̈al Tap: A Rockumentary by Martin Di Bergi) is a 1984 American mockumentary comedy film co-written and directed by Rob Reiner (in his feature directorial debut). The film stars Christopher Guest, Michael McKean and Harry Shearer as members of the heavy metal band Spinal Tap, who are characterized as "one of England's loudest bands". Reiner plays Martin "Marty" Di Bergi, a documentary filmmaker who follows them on their American tour. The film satirizes the behavior and musical pretensions of rock bands and the perceived hagiographic tendencies of rock documentaries such as The Song Remains the Same (1976) and The Last Waltz (1978), and follows the similar All You Need Is Cash (1978) by the Rutles. Most of its dialogue was improvised and dozens of hours were filmed.

This Is Spinal Tap was released to critical acclaim, but its initial release found only modest commercial success. Its later VHS release brought it greater success and a cult following. In 2002, it was deemed "culturally, historically, or aesthetically significant" by the Library of Congress, and was selected for preservation by the National Film Registry. It has been credited with "effectively" launching the mockumentary genre.