For decades, researchers have tried to identify ecological and biological correlates of longevity, often using life expectancy and maximum lifespan as the gold standards. The recent increase in demographic data collected in non-model species has also led researchers to develop alternative metrics of longevity, especially in comparative analyses (e.g. 90% longevity). As a result, studies focused on longevity rely on heterogeneous statistical methodologies and use a variety of longevity metrics that are not always clearly defined. This lack of clarity has led to confusion in the interpretation of results and makes it difficult to compare results across studies. This chapter discusses the statistical interpretation of each metric and highlights potential biases associated with the missus of longevity metrics; conducts a systematic review of the various longevity metrics used across the scientific literature and analyses the content of scientific articles on longevity using topic modelling methodology; and illustrates, using two examples, the importance of selecting the appropriate metric based on the research question. Based on these insights, it provides a list of recommendations aimed at helping researchers to think carefully about the choice of metrics when studying longevity.