Hepatitis B virus (HBV) is of universal concern: currently, around one-third of the global population (ca. 2 billion people) is, or has been, infected by HBY, it is estimated that there are 350-400 million chronic carriers and that half a million people die from HBV associated disease a year. This thesis investigates Hepatitis B Virus evolutionary dynamics, molecular epidemiology and molecular variants. First, Hepatitis B virus has presented a considerable challenge for evolutionary rate estimation. Here, this challenge is re-addressed using a novel analysis of newly acquired serial samples from the indigenous peoples of the South Pacific, in combination with previously published data. Second, using probabilistic Bayesian models to estimate evolutionary rates from noncontemporaneous sequences, as well as, phylogenetic methods for detecting recombination, the evolutionary history of hepatitis B virus was examined in the geographical region of Oceania; evolutionary rates, dates of divergence, as well as, genotype distributions are investigated. Finally, to investigate if Hepatitis B virus is a reemerging disease in the developing nations of the South Pacific the epidemiological status in the region was examined in two overlapping surveys. In the first survey the efficacy of the Hepatitis B virus vaccination programme was examined in three Pacific Island Countries: Papua New Guinea, the Republic of Fiji Islands and the Republic of Kiribati. e In the second survey 562 randomly selected human serum samples from Madagascar, Indonesia and Oceania are screened for naturally occurring surface gene variants of Hepatitis B virus. A combination of serological and nucleic acid testing techniques are used to determine both the apparent and hidden, historical as well as contemporary, incidence of HBV in the region.