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The Lightweight Directory Access Protocol (LDAP; /ˈɛldæp/) is an open, vendor-neutral, industry standard for accessing and maintaining distributed directory information services over an (IP) network.Directory services play an important role in developing intranet and Internet applications by allowing the sharing of information about users, systems, networks, services, and applications throughout the network. As examples, directory services may provide any organized set of records, often with a hierarchical structure, such as a corporate email directory. Similarly, a telephone directory is a list of subscribers with an address and a phone number.

LDAP is specified in a series of Internet Engineering Task Force (IETF) Standard Track publications called Request for Comments (RFCs), using the description language ASN.1. The latest specification is Version 3, published as RFC 4511.

A common use of LDAP is to provide a central place to store usernames and passwords. This allows many different applications and services to connect to the LDAP server to validate users.

LDAP is based on a simpler subset of the standards contained within the X.500 standard. Because of this relationship, LDAP is sometimes called X.500-lite.

Telecommunication companies' understanding of directory requirements were well developed after some 70 years of producing and managing telephone directories. These companies introduced the concept of directory services to information technology and computer networking, their input culminating in the comprehensive X.500 specification, a suite of protocols produced by the International Telecommunication Union (ITU) in the 1980s.

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