In the summer of 1944, at a dedication ceremony at Harvard's Cruft Laboratory, one of the world's first automatic digital calculating machines was unveiled to the public. The machine was the Automatic Sequence Controlled Calculator, more commonly known as the Harvard Mark I. The staff of the Harvard Computation Laboratory was unprepared for the interest which news of the machine's dedication touched off, and in response to many inquiries they arranged for the publication of this Manual of Operation. If the Mark I itself was a milestone in digital computing, so was this Manual: it was one of the first publications to address the fundamental question of how to get a computer to solve problems. Scattered throughout the book are listings of operation codes that represent sequences of operations the Mark I would carry out: these are among the first examples anywhere of what are now called computer programs. Both this Manual of Operation and the computer it describes reveal the profound transition from an age when computing was something human beings did, with varying degrees of mechanical aids, to one where machines themselves do most of the work.