This thesis uses the tool of mathematical modelling to address timely research questions in
the field of HIV and sexually transmissible infections (STI) population health. An evaluation
of the drivers of epidemics in South East Asia and Australia is conducted along with
projection of epidemic trajectories according to various scenarios. Economic implications of
public health and clinical decisions in HIV and STI control and care are also assessed. The
main chapters of this thesis have been reproduced from papers that have been published or
submitted for peer-review. The citations to these papers are provided at the start of each
chapter. At the time of writing, Chapter 1 had not yet been published but was in preparation
for submission to an international scientific journal. Content of all chapters appear as
published but minor alterations were made to the format of the papers; these include the
placement of figures and tables and references to supplementary material now refer to the
appropriate appendix. Reference styles were also changed to be made consistent throughout
the thesis.