Adhesive joints are widely used as a structural element in automotive and in aerospace applications because of their main advantage of more uniform stress distributions within lap joints relative to conventional bonding for example riveting or bolting. Adhesives can produce a stronger joint and potentially lengthen its service life. However, the stress distribution in the joint is not uniform and stresses are concentrated at the edges of the overlap. This can cause fatigue and reduce the service life of the joint. Therefore, a large number of analytical and numerical studies have been carried out to study this effect. Comparatively speaking, there is lack of experimental data to prove or cast doubt on the theoretical results. One of the main disadvantages of adhesive joints is that they have low durability when exposed to hostile environments. Moisture is the most commonly encountered service environment among various environmental conditions, to be considered a critical factor to affect the service life of adhesive joints. In this thesis, strain gauge, neutron diffraction, and X-ray diffraction methods have been used to directly investigate residual strains and stresses and also strains and stresses under tensile load in the adherends within adhesive joints. The residual strains and stresses have also been studied indirectly by means of a bimaterial method. In addition, the effect of moisture on the joints has been investigated by means of bimaterial and bulk adhesive samples. Neutron diffraction and bimaterial experiment results have been compared to FE predictions and good agreement achieved. The diffraction studies show that residual stress in joints due to manufacture are small and that water diffusion into the joint is a main critical factor affecting the performance of adhesive and adhesive joints.