Thyroid-specific enhancer-binding protein (T/EBP), also known as thyroid-specific transcription factor-1 (TTF-1), is a trans-activating transcription factor known to be involved in the tissue-specific expression of genes encoding thyroglobulin (TG), thyroid peroxidase (TPO), and thyrotropin receptor (TSHR) in the thyroid, and surfactant proteins A, B, and C, and Clara cell secretory protein in the lung. T/EBP is a homeodomain-containing DNA-binding protein found in the thyroid, lung epithelium, and specific areas of the forebrain during early embryogenesis. A mutant mouse lacking T/EBP expression was recently generated that is missing the thyroid, lung, ventral forebrain, and pituitary. These results clearly establish that T/EBP functions not only as a trans-activating factor to regulate expression of genes in the thyroid and lung, but also is required for the organogenesis of the thyroid, lung, ventral forebrain, and pituitary.