Nuclear receptors are ligand-activated transcription factors that bind to hormones such as oestrogen and progesterone, as well as a variety of other ligands, including vitamin D3 and prostaglandin J2. They form a large gene family — C. elegans alone has >270 members — and many have no known ligand. In Cell Science at a Glance, Marc Robinson-Rechavi and co-workers provide a brief introduction to these receptors, including a phylogenetic analysis of the known family members and a summary of their mode of action (see p. 585 +poster).