Ju-on is the title of a series of four horror films by Japanese director Takashi Shimizu. Shimizu attended the Film School of Tokyo, where he studied under Kiyoshi Kurosawa. Kurosawa helped Shimuzu shepherd the Ju-on projects to fruition.

The title of the films translates roughly to The Curse or The Grudge. The first two films in the series were made for video release only, but became surprise hits as the result of favorable word of mouth. The story is a variation on the classic haunted house theme, as well as a popular Japanese horror trope, the "vengeful ghost" (onryou). The curse of the title, ju-on, is one which takes on a life of its own and seeks new victims. Anyone who encounters a ghost killed by the curse is himself killed, and the curse is able to be spread to other areas.

Under very tight budgetary constraints, Shimizu's films garnered much acclaim from both critics and genre fans for their effective use of limited locations and eerie atmosphere to generate chills. Shimizu was at the same time perfectly willing to show his ghosts onscreen, in contrast to some directors who might choose only to hint at their appearance. But critics noted that Shimizu's minimalist approach to directing and storytelling a necessary by-product of the production's limited overall resources allows the films to retain their ability to unnerve viewers. Very few scenes in the movies are graphically bloody, making such scenes more disturbing when they occur.

Following the success of the two made-for-video films, and the international success of Hideo Nakata's Ringu (remade in the United States by Gore Verbinski as The Ring), Kurosawa and Ringu screenwriter Hiroshi Takahashi helped Shimizu develop Ju-on as a theatrical feature. This was released in 2002 to critical acclaim, and the US remake rights were purchased, with Sam Raimi, an ardent admirer of the original films, attached to direct. In 2003, a theatrical sequel, Ju-on 2, was released. The theatrical films retain the central premise of the direct-to-video films, but tell different stories.