Interactive Systems Corporation was a US-based software company and the first vendor of the Unix operating system outside AT&T, operating from Santa Monica, California. It was founded in 1977 by Peter G. Weiner, a RAND Corporation researcher who had previously founded the Yale University computer science department and had been the Ph.D. advisor to Brian Kernighan, one of Unix's developers at AT&T. Weiner was joined by Heinz Lycklama, also a veteran of AT&T and previously the author of a Version 6 Unix port to the LSI-11 computer.

Sixth Edition Unix, also called Version 6 Unix or just V6, was the first version of the Unix operating system to see wide release outside Bell Labs. It was released in May 1975 and, like its direct predecessor, targeted the DEC PDP-11 family of minicomputers. It was superseded by Version 7 Unix in 1978/1979, although V6 systems remained in regular operation until at least 1985.