Porous revetments made of crushed stones durably bonded by polyurethane or by any other type of binding material are increasingly used for coastal protection. Such revetments have several advantages as compared to conventional revetments. The crucial effect of the revetment porosity on the wave loading and the response of the structure has been illustrated by Liebisch et al. (2012). Though the revetment porosity may substantially be reduced over design life time (e.g. marine growth), the porosity is not yet explicitly and adequately considered in the current design practice. Therefore, the primary objective of this study is to improve the knowledge related to the effect of the porosity of a porous bonded revetment for different slope steepnesses on the hydrodynamic processes on and beneath the revetment. To achieve the objectives, extensive scale model tests have been conducted and a systematic analysis of the processes involved in the interaction of irregular waves and the porous revetment and its soil foundation is performed: (a) processes in front of and on the revetment (wave reflection, wave set-up and wave run-up/run-down); (b) wave-induced pressures on the revetment, (c) processes beneath the revetment such as the damping of wave-induced pressures in the revetment, the pore pressure in the sand core beneath the revetment, the internal mean water level and the stability of the sand core. Overall, the results have revealed for the first time the relative importance of the effect of the revetment porosity and slope steepness on all the processes involved in the interaction of irregular waves with a bonded porous revetment, thus providing an improved understanding of both effects. More specifically, it was shown for the first time that an increasing porosity leads to a larger effect of the incident wave height on the reflection coefficient. With increasing wave heights the highly porous revetment behaves increasingly like an impermeable revetment. A larger porosity also leads to lower values of both relative wave run-up and run-down with a more significant effect of the porosity on wave run-up. The spatial development of the internal mean water level in the sand core, which is decisive for the structure stability, was investigated systematically for irregular waves for the first time, showing that for the flatter slope 1:6 the internal wave set-up near the shoreline of the sand core is less affected by the swash processes than for the steeper slope 1:3.