The paper discusses the fundamental interaction between laser light and crystalline silicon within a broad range of laser parameters like wavelength and pulse length with relevance for cutting and drilling. For laser processing of silicon the absorption at the laser wavelength and the sensitivity of the material to thermal stresses are dominant. Using laser sources with corresponding wavelengths near the indirect band gap and with rising temperatures the optical behaviour of silicon changes significantly. A comparison of different pulse durations at the same wavelength from ultra short picosecond laser pulses up to continuous wave laser radiation is presented. The material removal processes like melt ejection, vaporization, and cracking by thermally induced stresses are studied. The influence of the laser radiation wavelength on the processing is investigated. The relevance of this work for some applications, like wafer dicing in the electronics industry and photovoltaic applications will be discussed briefly.