Researchers interested in obtaining detailed information on SNPs now work in a golden age of online database availability: never has so much data and such a wealth of information been freely accessible for such a substantial proportion of the 18 million single nucleotide polymorphism (SNP) loci currently characterized in the human genome. This chapter describes the major SNP databases available for human genetics studies. Tools and strategies are outlined that can help researchers properly formulate a database query to be able to access the most appropriate information needed for their research aims, including medical or population genetics analysis--an approach that is getting increased attention given the expanding scale of online SNP data.