Site-specific transcription factors (TFs) recognise their target genes in a sequence- or conformation-dependent manor. In contrast to the basal TFs that are the general facilitators of gene expression, their site-specific interaction partners are tissue- or condition-specific. Thus, site-specific TFs constitute the major prerequisite for the modular expression programmes that drive metazoan development. This article deals with the computational identification of TFs (how to find them in genomes) and with online resources such as the FlyTF database of Drosophila site-specific TFs (how to find them online).