Abstract H∞ robust control design theory has been developed in the last decade and enables feedback control systems to be designed using low order models that would be robust to the inevitable modelling errors. This robustness property has led to H∞ design techniques being applied to solve practical problems occurring in industry. This paper will detail the application of the H∞ design technique to the control of a ship's roll motion, where the lack of well defined ship model data has traditionally caused difficulties in ship control system design.