In the field of molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor) is a protein that binds to specific DNA sequences and thereby controls the transfer (or transcription) of genetic information from DNA to mRNA. Transcription factors perform this function alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase (the enzyme which performs the transcription of genetic information from DNA to RNA) to specific genes.

A defining feature of transcription factors is that they contain one or more DNA binding domains (DBDs) which attach to specific sequences of DNA adjacent to the genes that they regulate. Additional proteins such as coactivators, chromatin remodelers, histone acetylases, deacetylases, kinases, and methylases, while also playing crucial roles in gene regulation, lack DNA binding domains, and therefore are not classified as transcription factors.

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