This work reviews the physical basics and technical prerequisits of laser-induced interstitial thermotherapy (LITT) of brain structures. Laser-tissue interaction in the framework of LITT is predominantly based on absorption mediated thermal effects. Therefore, the optical and thermal properties of irradiated tissue are of major importance. These data are employed to predict the irradiation effects. In addition, they allow to develop appropriate applicator devices. Finally, the detailed knowledge about the irradiation process allows to define suitable monitoring techniques for LITT.