High pressure-high temperature techniques are used to synthesise new solid state compounds and materials that can be developed for technological applications. Laboratory and synchrotron x-ray diffraction and optical spectroscopy are combined with ab initio calculations to determine the structures and properties of new materials. We describe recent work on major classes of new materials including boron-rich solids, transition metal nitride superconductors, nitride spinels and light element solids based in the C–N–H system using examples from our own work.