In this paper the advantages of the realisation of a far infrared (FIR) free electron laser (FEL) are shown: it requires an electron beam with less stringent characteriaties, less expensive and it is unique source for nonlinearity and coherence in FIR. The dependence of the FEL performance en parameters of the electron beam and undulator is described. For a given beam emittance there is a specific wavelength below which the gain rapidly becomes very low. The important physical phenomena in the FIB and possible uses of FIRFEL are given in broad outline, these studies could be important for the possible development of a THz electronics.