Macro vulnerability of the small island developing states (SIDS) as well as of least developed countries (LDCs) has been an increasing concern for the international community. This has led to the design of an economic vulnerability index (EVI) to assess the structural economic vulnerability resulting from natural or external shocks. We first explain how vulnerability affects growth, development and poverty reduction, particularly in small developing countries. We then examine how the EVI has been designed and how it can be used to compare SIDS and LDCs. We argue that EVI is a relevant tool not only for identification of LDCs, but also for geographical aid allocation to favour vulnerable countries, including LDCs and SIDS, even though not all SIDS qualify as LDCs.