Directory services are a critical part of your identity infrastructure. Many components in the identity stack need to either read or write data. While any database could work, a popular choice for many identity projects is LDAP. This chapter is not a comprehensive guide to LDAP. If you are deploying LDAP in your environment, study the documentation for your LDAP Server of choice. Like other chapters in this book, the goal here is to give an overview of the technology and brief descriptions of some open source software tools.