Understanding the development and function of the prostate requires elucidation of the mechanisms through which genes are specifically activated in the prostate and the means by which they are regulated. Studies of development in many systems has led to a model showing that control of gene expression is exerted through three types of sequence region. The area immediately upstream or overlapping with the start site of transcription, the promoter, is important in defining the point(s) where transcription starts and, through the binding of specific transcription factors, may be involved in basal levels of transcription, responses to hormones or other regulatory factors, or in the tissue specificity of the gene’s expression. Enhancers are sequence regions separate from the promoter that act to increase the level of transcription from a promoter. They may be located upstream or downstream of a gene or within an intron, and characteristically their action is independent of their orientation and position relative to the promoter and is relatively independent of distance. In many cases, enhancers confer strongly tissue-specific expression, and they may exhibit significant selectivity in the promoters they activate. A third class of regulatory sequence is the locus control region (LCR). LCRs control the activation of sets of genes and are typically located at a significant distance from them (e.g., 50 kb). Their role is believed to be in the opening up of regions or domains of chromatin.