The behavior of carbon fibre reinforced polymer (CFRP) composite bonded to a steel plate double-lap joint was investigated experimentally. A total of 19 specimens were tested with the major test parameters being the bonded lap length, L, and the axial adherend stiffness ratio, ETR. Five of the 19 specimens were prepared using CFRP sheets, and the rest using CFRP plates. Two CFRP plate specimens were prepared with a tapered lap joint, and their results were compared with those of counterpart specimens prepared without tapered lap joints. In general, the behavior of specimens made from either CFRP sheets or CFRP plates were similar. The joint's axial load carrying capacity increased with increasing L up to a certain limit, when the joint's load carrying capacity could no longer be increased by increasing L. However, experimental results showed that a larger failure deformation could be achieved by increasing L past this limit. Specimens that had the same inner adherend thickness but higher axial adherend stiffness ratios showed higher axial load carrying capacities. Test results also showed that the strengths of tapered lap joints were almost the same as those of nontapered lap joints with the same L. Nonlinear finite element analysis was carried out to study the stress-strain, behavior of the adherend and the adhesive of the double-lap joint. Using finite element analysis results in an analytical solution obtained from the literature, predictions of the joint's maximum axial strength and minimum, required L were made. This analytical solution provided good predictions when, compared with test results, producing test to predicted ratios from 0.88 to 1.14. © 2007 NRC Canada.