Step Across the Border (1990), A ninety minute celluloid improvisation by Nicolas Humbert and Werner Penzel.

Step Across the Border is a 1990 avant-garde documentary film on English guitarist, composer and improviser Fred Frith. It was written and directed by Nicolas Humbert and Werner Penzel and released in Germany and Switzerland. The film was screened in cinemas in North America, South America, Europe and Japan, and on television in the United States, Germany, Switzerland, Austria and France. It was also released on VHS by RecRec Music (Switzerland) in 1990, and was later released on DVD by Winter & Winter (Germany) in 2003.

Shot in black and white, the 35mm documentary was filmed between 1988 and 1990 in Japan, Italy, France, Germany, England, the United States and Switzerland, and shows Frith rehearsing, performing, giving interviews and relaxing. Other musicians featured include René Lussier, Iva Bittová, Tom Cora, Tim Hodgkinson, Bob Ostertag and John Zorn.

The film won "Best Documentary" at the European Film Awards in 1990. A companion soundtrack album, Step Across the Border was also released by RecRec Music in 1990.

Step Across the Border is subtitled: A ninety minute celluloid improvisation by Nicolas Humbert and Werner Penzel.

"Improvisation" here refers not only to the music, but also to the film itself. Humbert and Penzel state in the 2003 DVD release of the film:

“In Step Across the Border two forms of artistic expression, improvised music and cinema direct, are interrelated. In both forms it is the moment that counts, the intuitive sense of what is happening in a space. Music and film come into existence out of an intense perception of the moment, not from the transformation of a preordained plan.”

The film is not narrated, and the musicians, the music and the locations are not identified. Instead it is a sequence of "snapshots' taken of Frith and musicians he has worked with, rehearsing and performing, interspersed with apparent random images of movement (trains, cars, people, grass) that blend in with the music. The improvised nature of the film and its direct cinema approach make it more of an art film than simply a documentary on a musician.

The music in the film is performed by Frith on his own, with others, and by others on their own. Some of the music is improvised, some is composed material performed "live", and some is previously recorded material played as accompaniment to many of the "movement" sequences in the film.

The recording of the film coincided with the formation and activity of Frith's review band Keep the Dog (1989–1991), and many of the participants of the band appear in the film. There are even a few rare glimpses of the band rehearsing. René Lussier in particular, features prominently and "interviews" Frith about his musical upbringing and approach to music.

The title of the film comes from the lyrics of the song "The Border", recorded by Skeleton Crew on their album, The Country of Blinds (1986). A brief "video" of this song also appears in the film.