The genome of hepatitis B virus (HBV) is a circular DNA molecule approximately 3,200 base pairs (bp) in length. Relative to other double-stranded DNA viruses capable of independent replication, HBV possesses the smallest genome of any virus known to infect man. Therefore, it is not surprising that HBV utilizes its genetic material economically. This is accomplished by two rare genetic arrangements: proteins are encoded from overlapping translation frames, and all regulatory signal sequences reside within protein-encoding sequences. Thus, HBV obtains multiple use from many regions of its genome, which underscores the sophistication of this virus from an evolutionary standpoint.