John Sheridan Thomas devoted most of his professional career to management consulting, as an associate with Booz, Allen and Hamilton New York, NY then as a partner of Devonshire Associates, Cambridge, MA. He is the author of the widely acclaimed "So Mr. Mayor, You Want to Improve Productivity...", published in 1974 by the National Commission on Productivity in cooperation with the Ford Foundation. Mr. Thomas has been a casual bridge player since the 1950's, but 15 years ago he began to study the game in depth, becoming a bridge teacher (accredited by the American Bridge Teachers Association and the American Contract Bridge League) and club director. Many of the bidding methods embodied in Standard American 21 were tested an validated through application of probability statistics and analysis of millions of random deals (computer-assisted of course - a tool not available when Goren and his contemporaries worked out bidding rules on table napkins). Consequently he was the first bridge authority to: Recognize the explicit value of a good five-card suit to notrump contacts. Define more precise sequences to exploit the full potential of five-card majors. Quantify the large advantage weak two bids have over their predecessors, the strong two openers and strong jump overalls. Mr. Thomas authored a variety of bridge articles published in ABTA Quarterly and in Bridge Today, and he is the editor of Bridge Snaps, an e-mail publication of bridge tips and humor. Here in Standard American 21 he presents an integrated bidding system built upon Goren's basics of 50 years ago, bringing together the best and most widely recognized innovations since then. This contemporary bidding system is in some ways simpler than the earlier standard, and in a great many ways more precise.