NFκB, a pleiotropic transcription factor, is present in almost all cell types and is involved in many biological processes including inflammation, immunity, differentiation, cell growth, tumorigenesis and apoptosis. NFκB is a homo- or heterodimeric complex formed by the Rel-like domain-containing proteins RELA/p65, RELB, NFκB1/p105, NFκB1/p50, REL and NFκB2/p52. This complex is controlled by various mechanisms of post-translational modification and subcellular compartmentalization as well as by interactions with other cofactors or corepressors. NKAP (NF-κ-B-activating protein) is a 415 amino acid nuclear protein that regulates TNF and IL1-induced NFκB activation. As component of a DNA-binding complex, NKAP also functions as a transcriptional repressor that acts on NOTCH target genes. Loss of NKAP blocks the development of αβT- cells, suggesting that it is required for their maturation through repression of NOTCH genes.