Construction of chimaeric MVA is a useful tool with which to study gene function of related viruses. The protocol given here describes MVA chimaeras containing genes from Fowlpox virus (FWPV), although this can be applied to DNA derived from other organisms. There are a number of steps required to make the chimaeric MVA: 1) Purification of viral particles; 2) Extraction of DNA from purified viral particles; 3) Assembly of linear recombination templates; 4) Transfection of linear recombination templates; 5) Selection of chimaeric MVA. Note: This procedure uses live virus, and should be conducted using Good Microbiological Practice, in accordance with international and national biocontainment requirements. This procedure also involves Genetic Modification of microorganisms, and appropriate safety approval should be obtained before commencing.