Tool use is a vital component of the human behavioural repertoire. The benefits of tool use have often been assumed to be self-evident: by extending control over our environment, we have increased energetic returns and buffered ourselves from potentially harmful influences. In recent decades, however, the study of tool use in both humans and non-human animals has expanded the way we think about the role of tools in the natural world. This Theme Issue is aimed at bringing together this developing body of knowledge, gathered across multiple species and from multiple research perspectives, to chart the wider evolutionary context of this phylogenetically rare behaviour.