IKKbeta/IKBKB (IkappaB kinase beta), also designated as IKK2, was named after its function of phosphorylating IkappaB molecules, the inhibitors of NF-kappaB transcription factors. The kinase activity of IKKbeta targets two adjacent serine residues of IkappaB leading to ubiquitination and proteasomal degradation of the inhibitor, followed by release and activation of NF-kappaB. Many signaling pathways that activate NF-kappaB converge at the level of IKKbeta. Examples of stimuli leading to IKKbeta and subsequent NF-kappaB activation include inflammatory cytokines (IL-1, TNFalpha), endotoxins (lipopolysaccharide), viral infection and double strand RNA as well as physical signals such as UV-irradiation. Transcription factors of the NF-kappaB protein family have a great variety of functions in regulating the immune system, cellular differentiation, survival and proliferation. NF-kappaB is an essential factor in acute as well as chronic inflammation, a pathological state which is either cause or co-factor in a great variety of diseases. Moreover, recent data suggest that many variants of cancer are characterized by elevated constitutive activity of NF-kappaB, which can act as a survival factor for malignant cells by its predominantly anti-apoptotic function. Given the tight regulation of NF-kappaB by IkappaB molecules and the central role of IKKbeta in phosphorylation and degradation of the inhibitor, IKKbeta is a very promising target for pharmaceutical substances aiming at interfering with NF-kappaB activation.