Investigation of theoretical aspects of the fundamental physical mechanisms that characterise heating of solids (i.e. semiconductors, metals, dielectrics) with ultrashort-pulsed lasers. Special emphasis is given on the induced surface modification (i.e. investigation of conditions for formation of periodic structure formation such as ripples, grooves, spikes) of solids. Regarding modelling of the underlying processes, a thorough investigation of physical processes on various temporal and spatial scales (multiscale modelling) is performed including mechanisms related to electrodynamics, electron excitation, nonthermal electron distribution, ultrafast dynamics and relaxation processes, phase transitions and hydrodynamics and elasto-plastic effects.