Genomic imprinting is an epigenetic mechanism of regulation that restrains the expression of a small subset of mammalian genes to one parental allele. The reason for the targeting of these approximately 80 genes by imprinting remains uncertain. We show that inactivation of the maternally repressed Zac1 transcription factor results in intrauterine growth restriction, altered bone formation, and neonatal lethality. A meta-analysis of microarray data reveals that Zac1 is a member of a network of coregulated genes comprising other imprinted genes involved in the control of embryonic growth. Zac1 alters the expression of several of these imprinted genes, including Igf2, H19, Cdkn1c, and Dlk1, and it directly regulates the Igf2/H19 locus through binding to a shared enhancer. Accordingly, these data identify a network of imprinted genes, including Zac1, which controls embryonic growth and which may be the basis for the implementation of a common mechanism of gene regulation during mammalian evolution.