This book gives emphasis to the various applications of Bacterial Artificial Chromosomes (BACs) in various studies. The topics presented are - using BAC libraries as assets for the mapping of marsupial and monotreme gene and for comparative genomic studies, and the usage of BACs as vehicles for maintaining the large infectious DNA genomes of viruses. The huge size of the insert DNA in the BACs and the ease with which engineering mutations in that DNA within the bacterial host can be achieved, allowed the manipulation of the BAC-viral DNA of Varicella-Zoster Virus. Some other issues that are discussed in the book are the maintenance and suitable expression of foreign genes from a Baculovirus genome; creation of multi-purpose clones of the same in the host of the new Bacillus subtilis etc. Furthermore, it caters to the use of the above to address important issues of gene regulation in vertebrates, such as functionally identifying novel cis-acting distal gene regulatory sequences.