The biology of the American plaice (the 'balai'), Hippoglossoides platessoides and its fishery in the N-W Atlantic are examined. A. Biology of the balai in relation to the fishery; (1) General distribution and maximum concentration. (a) Greenland, (b) Labrador, (c) Newfoundland, (d) Gulf of St. Lawrence, (e) Nova Scotia and U.S.A. (2) Factors influencing distribution. (a) Nature of bottom, (b) depth, (c) temperature. (3) Size distribution. B. The N-W Atlantic fishery. (1) Small-time fishery. (2) Commercial fishery. (3) Foreign fishery. C. Processing and marketing.