The new field of 'stoichiogenomics' integrates evolution, ecology and bioinformatics to reveal surprising patterns of the differential usage of key elements [e.g. nitrogen (N)] in proteins and nucleic acids. Because the canonical amino acids as well as nucleotides differ in element counts, natural selection owing to limited element supplies might bias monomer usage to reduce element costs. For example, proteins that respond to N limitation in microbes use a lower proportion of N-rich amino acids, whereas proteome- and transcriptome-wide element contents differ significantly for plants as compared with animals, probably because of the differential severity of element limitations. In this review, we show that with these findings, new directions for future investigations are emerging, particularly via the increasing availability of diverse metagenomic and metatranscriptomic data sets.