The timing of flowering initiation depends on the balanced expression of a complex network of genes that are regulated by both endogenous and environmental factors. We showed previously that mutations at the EARLY BOLTING IN SHORT DAYS (EBS) locus of Arabidopsis result in an acceleration of flowering, especially in noninductive photoperiods (short days), and other phenotypic anomalies. We have identified the EBS gene and demonstrate that it encodes a nuclear protein that contains a bromoadjacent homology domain and a plant homeodomain Zn finger. Both types of motif are thought to mediate protein–protein interactions and occur in transcriptional regulators involved in chromatin remodeling, suggesting that EBS is part of a transcriptional repressor complex that modulates chromatin structure and is required to repress the initiation of flowering in short days. Overexpression of EBS has phenotypic effects similar to those of recessive ebs mutations, suggesting that both might disrupt the formation of protein complexes that contain EBS. Analysis of the expression of flowering-time genes in ebs mutants and in EBS-overexpressing plants indicates that EBS participates in the regulation of flowering time by specifically repressing the expression of FT, a key gene in the integration of floral promotion pathways in Arabidopsis.