Blimp-1 (B lymphocyte-induced maturation protein) is a nuclear zinc-finger containing transcriptional repressor which primarily controls the terminal differentiation of mature B cells to plasma cells, and also involves in macrophage as well as T-cells population homeostasis/differentiation. It is also called positive regulatory domain I-binding factor-1 (PRDI-BF1) or PR (PRDI-BF1-RIZ) domain zinc finger protein 1 (PRDM1) and its first human homolog, PRDI-BF1, was identified by its ability to bind to the PRDI element on the IFN-beta promoter leading to inhibition of virus-mediated IFN-beta production. Blimp-1 contains N-terminal PR/SET domain and five C2H2 zinc fingers located near its C-terminus that mediate DNA binding, nuclear import and recruitment of histone modifying enzymes, and these activities enable Blimp-1 for its ability to control cell-fate decisions in the embryo and govern tissue homeostasis in multiple cell types in the adult organism. Blimp-1 recruits chromatin-modifying enzymes including HDACs and methyltransferases, and some of its target genes include c-Myc, CIITA, Pax5, Spi-B, and Id3. Blimp-1 sumoylation at Lys-816 by PIAS1 augments transcriptional repressor activity, and is critical for plasma cell differentiation. Deletion mutation of Blimp-1 is frequently observed in several tumors including lymphoid malignancies and has been proposed to be a candidate of tumor suppressor gene.