This chapter examines the genetic barcode, a standardized sequence of DNA used to identify species, in relation to its complex historical continuities. On one hand, the barcode is a product of the enduring drive to name and classify life on Earth. DNA is extracted from new and old specimens, the latter often to be found in natural history collections, and is transformed into barcodes that then populate new databases. Each animal species is meant to be furnished with this novel unique identifier to facilitate research and management. Advocates of the barcoding method thus regard it as establishing a new and better kind of certainty in relation to knowing species. On the other hand, the barcode joins a set of informational artefacts, including database records, species inventories and collection catalogues, that have become sites of contestations. Missing data, metadata and colonial categories invite us to unravel the wider data formations which capture and shape biological things. Rather than providing unequivocal identification or complete documentation, these artefacts evidence the institutional contingencies characterizing the collection and classification of lives. The chapter discusses three so-called data moments – a database record, a page from a museum inventory and the method section of a scientific paper – in order to draw out these historical continuities and trouble the promises of data-based certainty.