Weed invasion significantly threatens Australia's natural ecosystems and farming production. In order to reduce impacts of invasive weeds on Australia's natural assets, it is important to understand their origins, pathways of arrival and patterns of spread across the continent. It is very difficult to track weed invasion in real time, especially for species that have been resident in the invaded range for many decades or hundreds of years. Novel genetic techniques are emergening as powerful tools in understanding invasion pathways by examining genetic relatedness amongst weed populations in both the introduced and native ranges. Genetic tools may also reveal the ways in which weeds spread, for example whether or not they sexually reproduce seeds or spread clonally via stem or root fragments.