Forkhead box proteins (FOX proteins) play important roles in regulating the expression of genes involved in cell growth, proliferation, differentiation, and longevity. Many FOX proteins are important to embryonic development.

The defining feature of FOX proteins is the forkhead box, a sequence of 80 to 100 amino acids forming a motif that binds to DNA. This ability to bind to DNA allows FOX proteins to regulate the expression of target genes.

One of the most famous FOX protein genes is FOXP2 as it has been implicated in the acquisition of grammatical skills.

Many other genes encoding FOX proteins have been identified. For example, the FOXF2 gene encodes forkhead box F2, one of many human homologues of the Drosophila melanogaster transcription factor forkhead. FOXF2 is expressed in lung and placenta.

Some FOX genes are downstream targets of Sonic hedgehog (Shh) signaling. This is significant because Shh signaling plays a role in the development of basal cell carcinomas.