A method to predict the strength of adhesively bonded single and double lap joints from pultruded GFRP composite adherends subjected to quasi-static axial tensile loading is presented. The method is based on a quadratic through- thickness shear-tensile interaction failure criterion. The failure criterion was deduced from measured combined through-thickness tensile and shear strength values in the outer fiber-mat layer of the adherends (locations of the ultimate failure). The experimental strength values were obtained from a new shear-tensile interaction device (STI- device), which allows the measurement of shear-tensile interaction strength values. The predicted joint strengths corresponded well to the measured joint strengths of adhesively bonded single and double lap joints with different geometrical configurations. The investigation also showed that the material strength depended on the expansion of the stressed surface. The resistance against local stress peaks was much higher than the resistance against large uniformly distributed stress blocks. The application of the ultimate failure load prediction method showed a small influence of the adhesive layer thickness on the joint strength although the influence of the fillet radius was seen to be much higher. A partial material safety factor for the joint strength of 1.34 was determined. [All rights reserved Elsevier]