The H19 gene produces a non‐coding RNA, which is abundantly expressed during embryonic development and down‐regulated after birth. Although this gene was discovered over 20 years ago, its function has remained unclear. Only recently a role was identified for the non‐coding RNA and/or its microRNA partner, first as a tumour suppressor gene in mice, then as a trans‐regulator of a group of co‐expressed genes belonging to the imprinted gene network that is likely to control foetal and early postnatal growth in mice. The mechanisms underlying this transcriptional or post‐transcriptional regulation remain to be discovered, perhaps by identifying the protein partners of the full‐length H19 RNA or the targets of the microRNA. This first in vivo evidence of a functional role for the H19 locus provides new insights into how genomic imprinting helps to control embryonic growth.