ExPASy [1,2] (the Expert Protein Analysis System) is a World Wide Web server (http://www.expasy.org) which is provided as a service to the Life Sciences community. Its main focus is on proteins. It provides access to a variety of databases and analytical tools dedicated to what is now known as proteomics. It is developed at the Swiss Institute of Bioinformatics (SIB) (http://www.isb-sib.ch) by a multidisciplinary team. It first started to operate in August 1993 and has been running without interruption since that date. It seems to have been the first WWW server to be established in the field of life sciences. In December 2002 it had been accessed 242 million times by a total of more than 3 million computer hosts from 185 countries. We describe here what are the information resources and tools available on ExPASy.