Tumor necrosis factor (TNF) is a critical cytokine, which contributes to both physiological and pathological processes. This mini-review will briefly touch the history of TNF discovery, its family members and its biological and pathological functions. Then, it will focus on new findings on the molecular mechanisms of how TNF triggers activation of the NF-κB and AP-1 pathways, which are critical for expression of pro-inflammatory cytokines, as well as the MLKL cascade, which is critical for the generation of ROS in response to TNF. Finally, this review will briefly summarize recent advances in understanding TNF-induced cell survival, apoptosis and necrosis (also called necroptosis). Understanding new findings and emerging concepts will impact future research on the molecular mechanisms of TNF signaling in immune disorders and cancer-related inflammation.