In this paper, a first step towards the definition of a unifying model based on the process zone concept has been attempted. The aim of the proposed model is to summarize the fatigue behaviour of composite bonded joints under mixed-mode (I+II) fatigue loading conditions focusing as close as possible on the actual damage mechanisms observed during the fatigue tests, which were found strongly dependent on the mode mixity. The proposed model has been verified on the experimental results obtained from double cantilever beam (DCB), end notch flexure (ENF) and mixed-mode bending (MMB) tests as well as from single-lap bonded joints. Finally, the model is successfully applied to the description of joint behaviour under static mixed-mode loading.