The Herpes simplex virus (HSV) amplicon was designed in our laboratory, as a defective virus vector, capable of shuttle delivery of DNA sequences and genes from prokaryotic to eukaryotic cells, tissues or organs. The HSV vector was termed "amplicon" to delineate the fact that it carried the cloned sequences of interest, within amplified concatemeric defective genomes, packaged in HSV virions. Employing the replication functions of their helper virus, the amplicons are wide tropic vectors, capable of entry, replication, and gene expression in varied types of cells, both in vitro, and in vivo. In this brief review, the amplicons will be revisited, beginning with studies of the naturally occurring defective genomes, where many of the virologic aspects of the system were established. Properties of the amplicon system and its components, will be enlightened. The cis acting functions required for amplicon propagation will be briefly described. This will follow with examples of our studies of prokaryotic, viral and eukaryotic DNA sequences, which were amplified and expressed within HSV defective genomes. Studies designed to examine the involvement of helper viruses will be described, including our analyses of host shutoff mutant helper viruses. Finally, recent studies of other laboratories will be reviewed, with emphasis on what appears to be the use of amplicons as neurotropic vectors, towards potential gene therapy.