The two basic decisions in designing a carbon fibre composite wing are the selection of materials and the form of construction to be employed. The paper outlines the programme objectives, the design requirements and the constraints imposed thereby, and then presents in some detail the principles used to arrive at these decisions. The materials choice is a compromise between technical, manufacturing, commercial and strategic factors. The form of construction is chosen to obtain substantial weight saving at acceptable manufacturing cost, paying particular attention to four technical factors which are found to dominate the design. These are: (i) design for integrity in the presence of built-in and accidentally induced stress raisers; (ii) design for structural stability; (iii) design for integrity in a service environment including the effects of humidity and elevated temperature exposure; (iv) design and test margins to give adequate allowance for anticipated variability of structural performance.