Members of the small Maf family (MafK, MafF, and MafG) are basic region leucine zipper (bZip) proteins that can function as transcriptional activators or repressors. They dimerize with other proteins and bind DNA to either represse or activate transcription depending on the dimer compositions. BACH1 and BACH2, heterodimerization partners of MafK, are members of a novel family of BTB/POZ-basic region leucine zipper (bzip) factors. BACH1 and BACH2 have significant similarity to each other in BTB domain and Cap ‘n’ collar-type bZip domain but are otherwise divergent. BACH1 appears ubiquitous, whereas BACH2 is restricted to monocytes, neuronal cells and is abundantly expressed in the early stages of B-cell differentiation. BACH2, a 841 amino acid polypeptide, is an Nrf2-related transcription repressor and a tissue-specific partner of the Maf oncoprotein family. In culture cells, BACH2 is localized to the cytoplasm through its C-terminal cytoplasmic localization signal (CLS). Oxidative stressors aborted the CLS activity and induce nuclear accumulation of BACH2, which mediates nucleocytoplasmic communciation to couple oxidative stress and transcription repression in mammalian cells. BACH2 heterodimerizes with MAZR through its BTB/POZ domain to activate transcription. BACH2 also plays an important role in the regulation of B cell development.