The tumor necrosis factor/receptor [TNF/TNFR] superfamily consists of more than 20 transmembrane proteins with conserved N-terminal cysteine-rich domains [CRDs] in the extracellular ligand binding region. Members have wide tissue distribution and play important roles in biological processes such as lymphoid and neuronal development, innate and adaptive immune response, and cellular homeostasis. The chapters of this book address some of the most interesting functions of the TNF/TNFR superfamily.