UniProt- Universal Protein Resource

If you want information about any protein sequence that you have, you can use UniProt and it will provide you all the information about that specific protein sequence. You can access UniProt at www.uniprot.org.

It is an universal protein resource that is available to anybody at any location. It is one of the most popular protein databases. You can access if for free. It contains millions of protein sequences and their detailed information. It has vast information about the biological function of proteins that is obtained from the research literary texts.
UniProt = EBI + SIB + PIR

EBI- European Bioinformatics Institute
SIB- Swiss Institute of Bioinformatics
PIR- Protein Information Resource

These three large institutes are providing various bioinformatics databases and services, like ExPasy. Expasy can only be accessed through UniProt website. UniProt is the sumtotal of all these protein databases.

It is completely true that UniProt is maintained and annotated by all of these members together. A short time ago, SIB and EBI together created Swiss-prot and TrEMBL databases. Not only this, PIR has also produced a protein sequence database that is named as PIR-PSD. Though, EBI,SIB and PIR are together maintaining UniProt, they also have other databases too. 

UniProt offers four basic databases:
1. UniProtKB
2. UniParc
3. UniRef
4. UniMes