Over the past decade, countries worldwide have observed the rapid emergence of substances collectively referred to as ‘new psychoactive substances’ (NPS). To date, hundreds of NPS have been identified; however, for the most part very little is known about these substances. The exponential growth of NPS, combined with uncertainty regarding potential harms, has generated considerable concern amongst policy makers and there is international consensus regarding the need for ongoing monitoring and research into the NPS market. However, much of the research conducted in this area originates from Europe and the United States, with Australian-specific studies relatively scarce. This thesis aimed to address this gap in Australian specific studies using two data sources: the 2013 National Drug Strategy Household Survey (NDSHS: a general population prevalence survey) and the Ecstasy and related Drugs Reporting System (EDRS: a national survey of high frequency stimulant consumers). Specifically, this thesis aimed to: 1) determine if there is a distinct group of exclusive Australian NPS consumers; 2) examine rates of use of different classes of NPS amongst people who use other illicit substances; 3) examine the motivations associated with NPS use; and 4) explore the purchasing and supply patterns of NPS consumers. A number of key findings emerged from this thesis. Firstly, using data from the NDSHS, it was found that there is no distinct group of exclusive Australian NPS consumers; rather they primarily consist of people using a range of illicit substances. Secondly, using data from the EDRS, it was found that the NPS market is highly dynamic, with the consumption of particular NPS classes changing over time. Thirdly, NPS use appears to be a marker for higher engagement in substance use, and as such, higher rates of drug-related risk behaviours. Finally, the collective findings of this thesis illustrate the heterogeneity of NPS consumers. Taken together, these findings suggest that specialised NPS interventions may be unnecessary; rather, existing health services should screen for and be equipped to deal with NPS-related presentations. Furthermore, the diverse and rapidly changing nature of the NPS market demonstrates the need for international collaboration, combined with a rapidly responsive health framework.