Since the first description of the cloning und mutagenesis of a herpesviral genome in 1997, a number of herpesviral DNA's have been cloned as bacterial artificial chromosomes (BACs). Herpesvirus BAC's are established by introduction of a mini F origin of replication into the viral genome, which can as such be maintained und manipulated in Escherichia coli as a single copy extrachromosomal DNA. Herpesvirus DNA's cloned as BAC's are accessible to the DNA repair und mutagenesis apparatus encoded by E. coli, which can be exploited for the generation und subsequent analysis of virus mutants. One of the advantages of BAC cloning und mutagenesis is that it is independent of virus growth in cultured cells, thereby minimizing the risk of compensatory mutations. Here we summarize BAC's that have been established for Herpesviruses of livestock, among them Bovine Herpesvirus Type 1 (BHV-1), Equine Herpesvirus Type 1 (EHV-1), Marek's Disease Virus (MDV), Pseudorabies Virus (PRV). Special emphasis is put on the exploitation of herpesviral BAC's for the analysis of virus replication und vaccine developments.