The awareness that protein and DNA sequence data are essential to the understanding of biological systems is now well established in the life science community. This community is progressively becoming conscious that this is also true of additional information about protein expression, post-translational modifications, tertiary structure and, of course, function. All of this knowledge needs to be encapsulated in various databases. The goal of this chapter is to describe the data resources that are available to researchers working in the field of proteome studies. We will not attempt here to survey all the different databases that are relevant to this field. Such an exercise would be tedious due to the large number of relevant databases and would only be valid for a very short period of time due to the extreme speed with which new databases are appearing and/or disappearing. It is also for this reason that you will find a table at the end of this chapter (Table 5.l) listing the World-Wide Web (WWW) addresses of the databases described in the following sections. The most important component of this table is the Internet address that allows you to download an upto- date version of the table! We will successively describe the type of information found in the following types of databases: protein sequence, nucleotide sequence, pattern/profile, 2-D PAGE, 3-D structure, post-translational modification, genomic and metabolic. The last section of this chapter will try to predict future trends in the evolution of protein information resources.