A major source of illicit financial flows (IFFs) out of developing countries accrues from the under-invoicing of commodity exports. This erodes the tax base of resource-rich developing countries, and hence their capacity to mobilise domestic resources for development. The Sustainable Development Goals (SDGs), adopted in 2015, specifically call on states to reduce IFFs and enhance domestic resource mobilisation. Yet a weak capacity to assess the magnitude and drivers of the phenomenon has limited the ability of developing countries to effectively curb IFFs. This has been compounded by a lack of consensus over IFF definitions together with poor data and weak methods. Drawing on six years of interdisciplinary research into commodity trade–related IFFs, this chapter examines novel data sources and recent methodological advances that researchers and regulators can draw upon to better capture and eventually reduce IFFs. It situates such advances within the fast-expanding literature on domestic resource mobilisation, taxation and IFFs, focusing on three major channels; namely, trade mispricing, abusive transfer pricing and tax evasion through wealth offshoring. The chapter concludes by discussing the scope for improved data collection and evidence generation. This, together with global taxation reform, can greatly contribute to effectively enhancing domestic resource mobilisation in developing countries.