Three independent databases of eukaryotic genome size information have been launched or re-released in updated form since 2005: the Plant DNA C-values Database (www.kew.org/genomesize/homepage. html), the Animal Genome Size Database (www. genomesize.com) and the Fungal Genome Size Database (www.zbi.ee/fungal-genomesize/). In total, these databases provide freely accessible genome size data for >10 000 species of eukaryotes assembled from more than 50 years’ worth of literature. Such data are of significant importance to the genomics and broader scientific community as fundamental features of genome structure, for genomics-based comparative biodiversity studies, and as direct estimators of the cost of complete sequencing programs.