Technical Abstract: Introduced species disrupt native communities and biodiversity worldwide. Parasitic infections (and at times, their absence) are thought to be a key component in the success and impact of biological invasions by plants and animals. They can facilitate or limit invasions, and positively or negatively impact native species. Parasites have not only direct effects on their hosts, but also indirect effects on the species with which their hosts interact. Indirect effects include density mediated effects (resulting from parasite-induced reduction in host reproduction and survival) as well as trait-mediated indirect effects (resulting from parasite induced changes in host phenotype, behaviour or life history). These effects are not mutually exclusive but often interact. Parasites are involved in interactions at all trophic levels, and may induce trophic cascades within their recipient community including the parasite community within an individual host. The importance of these interactions for invasion success, and the extent to which these indirect effects ramify throughout communities and influence ecosystems undergoing biological invasion is the focus of our synthesis. Examples from the animal and plant literature illustrate the importance of parasites in mediating both competitive and consumer-resource interactions between native and invasive species. The indirect effects of parasitic infection are important at a range of biological scales in determining invasion success and impact.