Forkhead box protein 1 (FOXP1) is a member of the Forkhead family of transcription factors, which have been characterized as transcriptional repressors and activators, and as having a DNA-binding domain distinguished by its formation of a winged-helix motif. FOXP1 is known to be an important regulator of airway morphogenesis, lung epithelial development, and early cardiac development. It is also known to have an important role in conjunction with NFκβ in the development of B-cells and the differentiation of macrophages. Splice variants give rise to four isoforms of FOXP1. The protein is known to form homodimers and heterodimers with FOXP2 and FOXP4. Studies have indicated FOXP1 as a potential inducer of oncogenesis when over expressed. The depletion and mutation of FOXP1 expression may lead to defects in embryonic cardiac, lung and esophagus epithelial development.