An account is given of important fundamentals, working methods, and recent results in the context of influenza virus genetics. Reference is made to the potentials implied in gene mapping and to the possibility of elucidating the correlations between the single gene and all biological properties of the influenza virus. Discussed against that background are the polyacrylamide electrophoresis of virus RNA, hybridisation with complementary RNA, immunological and chemical differentiation of gene products, as well as the use of defect mutants and of recombinant formation. It is shown that successful elucidation of the genesis of new virus strains is possible by means of those methods which also enable the preparation of virus strains with desired properties. This is likely to open up new horizons for more progress in the context of immunoprophylaxis against virus influenza.