There is provided apparatus and a method for assessing the integrity of a bonded joint and a bonded joint assembly. The assembly has a bonded joint monitored for bond integrity and comprises first (1) and second (2) components each defining a bonding surface (3,4); the joint (5) is formed between the bonding surfaces (3,4) and the first component (1) defines a passage (15) therethrough from the bonding surface to an exterior of the component. The joint (5) includes an optical fibre (11) extending along the joint (5) between the bonding surfaces, through the passage (15) and emerging from the passage (15) to the exterior of the component. The method of constructing the assembly includes the steps of passing the optical fibre (11) through the passage (15) and adhering the optical fibre (11) to the bonding surface (3) of the first component (1), thus bringing the two bonding surfaces (3,4) together and forming the bond (5).