The present invention relates methods of generating infectious negative-strand virus in host cells by an entirely vector-based system without the aid of a helper virus. In particular, the present invention relates methods of generating infectious recombinant negative-strand RNA viruses intracellularly in the absence of helper virus from expression vectors comprising cDNAs encoding the viral proteins necessary to form ribonucleoprotein complexes (RNPs) and expression vectors comprising cDNA for genomic viral RNA(s) (vRNAs) or the corresponding cRNA(s). The present invention also relates to methods of generating infectious recombinant negative-strand RNA viruses which have mutations in viral genes and/or which express, package and/or present peptides or polypeptides encoded by heterologous nucleic acid sequences. The present invention further relates the use of the recombinant negative-strand RNA viruses or chimeric negative-strand RNA viruses of the invention in vaccine formulations and pharmaceutical compositions.