One of the essential requirements of the proteomics community is a high quality annotated nonredundant protein sequence database with stable identifiers and an archival service to enable protein identification and characterization. The scope of this chapter is to illustrate how Universal Protein Resource (UniProt) (The UniProt Consortium, Nucleic Acids Res. 38:D142-D148, 2010) can be best utilized for proteomics purposes with a particular focus on exploiting the knowledge captured in the UniProt databases, the services provided and the availability of complete proteomes.