Of all the “-omes” in the world, here’s another one for your vocabulary: the reactome. Reactome.org is an excellent database of “reactions” in biology (as well as the biological pathways composed of those reactions). In contrast to the first definition of “reaction” that may come to mind (e.g. a biochemical reaction), Reactome.org more broadly defines “reaction” as any biological state change. The Reactome website is beautifully designed and comes fully equipped with a comprehensive user guide, pathway browser (which in turn has its own user guide), and analysis tool for user-uploaded data. Although human-centric, the Reactome database currently contains protein, reaction, and pathway information for twenty-one species spanning humans, mice, fruit flies, worms, yeasts, and plants. Users should be aware that pathway information for nonhuman species in the Reactome database includes both manually curated pathways and electronically inferred pathways from curated human pathways.