Homologous regions (hrs) are repeats of variable length interspersed in defined locations of most baculovirus genomes. They are characterized by tandem copies of motifs including an imperfect palindromic core. Although they present significant sequence similarity within a genome they are highly variable between species. In AcMNPV and other well studied baculoviruses hrs have been implicated as origins of DNA replication as well as enhancers for transcription of early genes. Expression from several promoters of either baculovirus origin or other sources can be stimulated by cis-linkeage to hrs in insect cells. There are evidences that support the involvement of cooperative action of both viral and host factors for promoting hr-mediated enhancing activity. Since its development, the baculovirus expression vector system, has become one of the most popular systems for the expression of heterologous proteins in a eukaryotic environment. In this system, high expression levels are driven from strong promoters by the viral RNA polymerase, at very late times of infection, when some cellular functions begin to decay. For cases in which proteins could be better expressed earlier, hrs appear to be versatile elements for engineering alternative baculovirus-derived expression systems. More recently, the potential of baculovirus to be developed as gene therapy vectors has renewed the interest for exploring possibilities to enhance early gene expression in order to augment their ability to transduce mammalian cells, where viral infection cannot progress.