Blood-brain barrier (BBB) genomics begins with the isolation of capillaries from fresh animal or human brain and is followed on the same day with the purification of capillary-derived RNA. The identification of microvascular-enriched genes from a whole brain gene microarray is unlikely because the brain capillary endothelial volume is <0.1% of total brain. Libraries of partial cDNAs corresponding to genes that are selectively expressed at the BBB are generated with polymerase chain reaction-based approaches such as subtractive suppressive hybridization. The availability of these partial cDNAs, in conjunction with production of animal or human BBB cDNA libraries, enables the cloning of the full-length cDNAs and a functional analysis of the BBB-enriched genes. The development of BBB genomics technologies enables the acquisition of a large body of new knowledge about the BBB and the brain microvasculature.