Usability engineering is the process whereby the usability of a product is specified quantitatively, and in advance. Then, as the product is built, testing takes place to see whether the planned-for levels of usability have been achieved. This paper describes the way that usability engineering has been implemented by a large engineering group building office software systems. The methods employed are described, and the measures that are taken. By means of two hypothetical product scenarios, it is demonstrated how usability testing is performed and the success that is achieved in feeding back early information to the software engineers. This feedback results in the improvement of the usability of the developing product. The paper ends with some guidelines for successful incorporation of usability engineering into the product development cycle.