The introduction of novel species to a region often results in biological invasions, a process occurring throughout the globe --- from the poles to equator and across land, wetland, river, and sea. Invasions provide exceptional opportunities to advance our knowledge of fundamental processes involving population biology, species interactions, community ecology, biogeography, ecosystem function, evolution, and adaptation. By occurring over relatively recent and measurable timescales, invasions provide opportunities to examine how species and ecosystems respond to new arrivals, and how species adapt to new environmental conditions. These types of “natural experiments” can provide new insights into many biological processes, especially early in the colonization process, that are not possible with native communities. SERC research examines invasion ecology at the population, community, and ecosystem level across a diverse range of habitats and organisms, both to advance basic science and inform management and conservation strategies.