Adhesive bonded joints are commonly used in structural applications. The thickness of the bondline has an important influence in the resistance of the joint. Information on this topic is mostly available for thin bondlines; up to 1 mm. However, little information is known about the effect of increasing the bondline thickness. This study consists of a literature study to analyze the trends on the mechanical properties such as shear strength, peel strength and fracture toughness due to increasing bondline thickness; an experimental part that studies the shear strength of double lap joints loaded in tension using one brittle and one ductile adhesive; and a numerical part that assesses whether the experimental results can be reproduced using Finite Element techniques. From the experiments, thickness dependency on multiple parameters such as the lap shear strength, the deformation capability and the strains at failure is proven. For both adhesives, the lap shear strength decreased with thickness. The Finite Element Analysis are able to accurately predict the failure initiation for the thick joints and the deformation capability up to yield for all the thicknesses.