Adenovirus genomes are linear, non-segmented double-stranded (ds) DNA molecules that are typically 26-46 Kbp long, containing 23-46 protein-coding genes. The example used for the following description is Human adenovirus E, a mastadenovirus with a 36 Kbp genome containing 38 protein-coding genes. While the precise number and identity of genes varies among adenoviruses, the basic principles of genome organization and the functions of most of the genes described in this article are shared among all adenoviruses. The 38 genes in the Human Adenovirus E genome are organized in 17 transcription units, each containing 1-8 coding sequences. Alternative splicing during processing of the pre-mRNAs produced by each transcription unit enable multiple different mRNAs to be produced from one transcription unit.