Transcription factors are central to the process of eukaryotic gene control. These proteins influence the basal level of gene expression in a cell and can modulate genetic programs by activating or repressing the transcription of particular genes in a cell-type specific or inducible manner. This book provides a state-of-the-art overview of the wide gamut of cellular and viral transcription factors, with emphasis on structure-function interrelations in the context of the nuclear environment, their modes of action in signal-dependent and tissue-specific gene regulation, and their involvement in various aspects of growth, differentiation and tumorigenesis/antioncogenesis.