Nuclear transcription factor-κB (NF-κB) is an important factor involved in inflammatory reactions. When a cell receives extracellular stimulation, the NF-κB in the cytoplasm is released and activated from a previously κB-inhibited status. The activated NE-κB then moves into cell nuclei and acts upon promoters of particular genes, resulting in expression of those genes. The expressed genes further lead to an inflammatory reaction, modulation of apoptosis, and initiation of carcinogenesis. It is necessary to elucidate the details of the roles of NF-κB in cell inflammation, apoptosis, and carcinogenesis. This review article discusses the constitution of the NE-κB family, interactions between NE-κB and programmed cell death, the regulating factors and mechanisms involved in activation of NE-κB, the relationship between NE-κB and carcinogenesis, the regulation of NE-κB via tumor-related proteins, and possible tumor treatment through the control of N F-κB.