Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling. Physiologically, S-nitrosylation regulates protein stability, activity, subcellular localization, and protein-protein interactions and plays important roles in maintaining cell homeostasis. However, aberrant S-nitrosylation is associated with diverse pathobiologies. Transcription factors are key molecules that bind to DNA-regulatory sequences (enhancers and silencers), usually localized in the 5'-upstream region of target genes, to regulate gene expression. Here we review the biochemical mechanisms underlying the S-nitrosylation of transcription factors, and discuss the multiple roles of S-nitrosylation in the regulation of gene transcription.