We build a composite index of formal sovereignty as an alternative to the binary classification ‘Sovereign vs Affiliated’ for the purpose of a comparative, quantitative analysis on a large sample of small islands. This index takes into account different degrees of sovereignty through the different attributes of sovereignty (diplomacy, executive, legislative,
judicial, defence, and monetary). We use a conservative method to code the components and to aggregate them, trying to stay as simple and objective as possible, while remaining transparent and laying the foundations for future improvements. The index is calculated for a
sample of 104 small islands and coastal territories. The results show that the binary classification based on United Nations (UN) membership is significantly limited, if not mistaken, because according to our index some territories which are not UN members have a higher sovereignty score than some UN members.