The Ebf (O/E) family of helix-loop-helix transcription factors plays a significant role in B lymphocyte and neuronal development. The three primary members of this family, Ebf1, 2, and 3, are all expressed in adipocytes, and Ebf1 promotes adipogenesis when overexpressed in NIH 3T3 fibroblasts. Here we report that these three proteins have adipogenic potential in multiple cellular models and that peroxisome proliferator-activated receptor gamma (PPARgamma) is required for this effect, at least in part due to direct activation of the PPARgamma1 promoter by Ebf1. Ebf1 also directly binds to and activates the C/EBPalpha promoter, which exerts positive feedback on C/EBPdelta expression. Despite this, C/EBPalpha is dispensable for the adipogenic action of Ebf proteins. Ebf1 itself is induced by C/EBPbeta and delta, which bind and activate its promoter. Reduction of Ebf1 and Ebf2 proteins by specific short hairpin RNA blocks differentiation of 3T3-L1 cells, suggesting a critical role for these factors and the absence of functional redundancy between members of this family. Altogether, these data place Ebf1 within the known transcriptional cascade of adipogenesis and suggest critical roles for Ebf1 and Ebf2.