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 including a securing section for securing the fastening extrusion to the existing wall structure, a first retaining wall structure near one end of the fastening extrusion and adjacent the securing section, the first retaining wall structure including a recess which receives one hook wall of the wall panel, and a second retaining wall structure near another end of the fastening extrusion, the second retaining wall structure including a recess which receives one hook wall of another wall panel.