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Abstract; Stratospheric ozone layer depletion, first observed in the 1980s, remains a persistent environmental issue. It has been caused by the increased production and use of substances such as chlorofluorocarbons (CFCs), halons and other chlorine- and bromine-containing compounds, collectively termed ozone-depleting substances (ODSs). Following controls on the production of major, long-lived ODSs by the Montreal Protocol, the ozone layer is now showing initial signs of recovery and is anticipated to return to pre-depletion levels in the mid-to-late twenty-first century. However, there is now growing evidence that a class of ODSs, known as Very Short-Lived Substances (VSLSs), could present a barrier to a timely ozone recovery. Uncontrolled emissions of a number of anthropogenic VSLSs (e.g. CH₂Cl₂) are adding significant amounts of ozone-depleting chlorine to the atmosphere, and biogenic emissions of brominated VSLSs (e.g. CHBr₃) are suggested to increase in a future climate. In this talk, I will present modelling work and observations to highlight the current state of science concerning VSLS emissions, their transformation in the atmosphere, along with their possible impacts on ozone and ozone recovery.