The need for greater bandwidth has driven laser manufacturers towards the use of distributed feedback semiconductor (DFB) lasers with a well-defined single mode. These semiconductor diode-based devices are now essential components in a broad range of advanced optical systems. This text covers the materials, operation and design strategies of DFB lasers. It provides detailed accounts of large-signal time-domain numerical modelling techniques, which can be extended to optical systems and components other than DFB lasers. Numerical MATLAB programs are outlined in the text.