In this chapter we aim to provide an overview of DNA variant databases, commonly known as Locus-Specific Databases (LSDBs), or Gene-Disease Specific Databases (GDSDBs), but the term variant database will be used for simplicity. We restrict this overview to germ-line variants, particularly as related to Mendelian diseases, which are diseases caused by a variant in a single gene. Common difficulties associated with variant databases and some proposed solutions are reviewed. Finally, systems where technical solutions have been implemented are discussed. This work will be useful for anyone wishing to establish their own variant database, or to learn about the global picture of variant databases, and the technical challenges to be overcome.