Nuclear factor-kappa B (NF-kappa B) and its activating signaling pathways are critical regulators for cell lineage development, growth, differentiation, apoptosis, and tumorigenic transformation. As one of the most important transcription factors, NF-kappa B has been implicated in the transcriptional upregulation of a number of cytokines, adhesion molecules, growth factors, oncogenes, antiapoptotic proteins, some proapoptotic factors, and even certain viral genes. The role of NF-kappa B on tumor promoting has been well-documented in the past two decades. However, during the past few years, a considerable number of studies suggested that NF-kappa B and its activating signaling molecules may act as tumor suppressors under some circumstances. Thus, it is highly possible that tumor promoting or tumor suppressing of NF-kappa B signaling is determined by the type of cells, stimuli, simultaneous or asynchronous intracellular signals, and other cellular contexts.