The cerebellum is a key brain region for motor control and coordination and its microcircuitry is a much-studied system in neuroscience. For researchers interested in understanding how the mammalian cerebellum develops, the Cerebellar Development Transcriptome Database (CDT-DB) is a great online resource. The website offers access to a database of spatiotemporal gene expression profiles for genes expressed in the developing cerebellum, drawing upon data from a variety of experimental approaches including in situ hybridization, cDNA microarrays, and RT-PCR. The “about” section of the website provides site visitors with a comprehensive overview of the CDT-DB Project, the database itself, and the methods used to collect data. While users can use the gene search option to search for individual genes, a perhaps more useful feature is the expression data search, wherein users can search for one or many of the following parameters: spatial expression, developmental temporal expression pattern, brain distribution, and brain specificity.