Pornography is a genre that involves the representation of sexually explicit scenarios and is created for the purpose of bodily arousal. The genre employs a particular set of conventions to distinguish "soft-core" from "hard-core" porn. The history of moving-image pornography can be traced from the earliest moments of filmmaking, including single-reel exhibitionist films common to primitive silent cinema. Over time, pornography moved from being exhibited in men's clubs (as stag films) to developing more elaborate narratives that were subsequently shown in grindhouse, sexploitation, and X-rated theaters across the United States. During the late 1970s, the US adult film industry was one of the first areas to take advantage of new videotape technology, and the consumption of sexually explicit materials moved from theatrical exhibition to the home. Since the onset of both digital video disc (DVD) production and Internet services, the production and distribution of pornographic film and video in the United States has grown into a multibillion dollar industry.
The history of moving-image pornography also includes an understanding of the legal parameters that tend to determine the representation, production, and distribution of the genre. The changing definition of obscenity plays an important role in delineating soft-core and hard-core pornography, and evolving cultural attitudes toward porn are connected to trajectories in the women's movement and gay and lesbian activism. In the twenty-first century, almost any sexual practice and/or fetish can be found represented in some niche of the soft-core and hard-core pornographic industry.