In order to use herpes simplex virus (HSV) as a vector for the transmission and expression of foreign genes, it is obviously necessary to be able to prepare stocks of the virus and to propagate both HSV and the recombinant viruses derived from it. Similarly, the introduction of foreign genes into the virus will require the purification of viral DNA for use as a cloning vector, and preparation and analysis of viral DNA will also be necessary in order to characterize the recombinant viruses produced during the cloning procedures. This chapter will therefore discuss in turn the procedures used in our laboratory for the growth of HSV, and for the preparation of viral DNA.