The single lap joint is the most studied joint in the literature in terms of both theory and practice. It is easy to manufacture and the lap shear strength is a useful parameter for strength assessment and quality control. Simple design rules exist such as the one described in ASTM 1002 standard or in a recent paper by Adams and Davies. A previous study by the present authors gave a simple predictive equation considering the type of adhesive, i.e. ductile or brittle, the adherend yield strength and the overlap length. However, other factors also affect the joint strength such as the adherend and adhesive thicknesses and the surface preparation which have not previously been addressed in the literature. In order to quantify the influence of the adhesive (toughness and thickness), the adherend (yield strength and thickness), the overlap and the surface preparation on the lap shear strength, the experimental design technique of Taguchi was used in the present study. An experimental matrix of eighteen tests was designed and each test was repeated three times. The influence of the six previously-mentioned variables could be assessed using the statistical software Statview (R). In this paper a simple predictive equation is proposed for the design of single lap joints. (C) Koninklijke Brill NV, Leiden, 2008