The conventional approach to through-life-support for aircraft structures can be divided into the following phases: (i) detection of defects, (ii) diagnosis of their nature and significance, (iii) forecasting future behaviour-prognosis, and (iv) pre­ scription and implementation of remedial measures including repairs. Considerable scientific effort has been devoted to developing the science and technology base for the first three phases. Of particular note is the development of fracture mechanics as a major analytical tool for metals, for predicting residual strength in the presence of cracks ( damage tolerance) and rate of crack propagation under service loading. Intensive effort is currently being devoted to developing similar approaches for fibre composite structures, particularly to assess damage tolerance and durability in the presence of delamination damage. Until recently there has been no major attempt to develop a science and tech­ nology base for the last phase, particularly with respect to the development of repairs. Approaches are required which will allow assessment of the type and magnitude of defects amenable to repair and the influence of the repair on the stress intensity factor (or some related parameter). Approaches are also required for the development and design of optimum repairs and for assessment of their durability.