In order to improve the understanding of the mechanisms of laser surface treatment and to optimize industrial applications, a general model of laser surface treatment has been accomplished which enables calculation of the thermodynamic phenomena and analysis of the process. With particular emphasis on laser cladding and alloying, powder heating has been investigated in detail, which can be divided into heating during travelling through the laser beam and subsequent heating by the melt pool. While the time scale of the former heating mechanism is of the order of 1 ms, pool heating takes place within 10 microsecond(s) , hence almost immediately. While the pool temperature determines whether powder will be melted or not, in principle any powder, even WC, can be melted when passing the beam, as long as the calculated threshold intensity range is exceeded. Laser cladded tracks prove to be determined by the melt pool shape which is calculated analytically for non-gaussian beams, as well. While for low powder feeding rates cladding is limited by the mass balance, for substantial powder delivery the energy balance turns out to be the limiting criterion, while dilution diminishes. Increased degree of overlap between two tracks decreases the roughness of the cladded surface.