A system for mounting wall panels to an existing wall structure, includes a plurality of wall panels, each wall panel having a main panel section and hook walls at edges of the main panel section, with the main panel section and each hook wall having a U-shaped cross-sectional profile. There are also a plurality of fastening extrusions. Each fastening extrusion includes a securing section for securing the fastening extrusion to the existing wall structure, and a retaining wall structure at one end of the securing section, the retaining wall structure including a recess which receives one hook wall of the wall panel.