The rule that the organization of the software and the organization of the software team will be congruent; commonly stated as “If you have four groups working on a compiler, you'll get a 4-pass compiler”. The original statement was more general, “Organizations which design systems are constrained to produce designs which are copies of the communication structures of these organizations.” This first appeared in the April 1968 issue of Datamation. Compare SNAFU principle.
The law was named after Melvin Conway, an early proto-hacker who wrote an assembler for the Burroughs 220 called SAVE. (The name ‘SAVE’ didn't stand for anything; it was just that you lost fewer card decks and listings because they all had SAVE written on them.) There is also Tom Cheatham's amendment of Conway's Law: “If a group of N persons implements a COBOL compiler, there will be N-1 passes. Someone in the group has to be the manager.”