OpenID is a shared identity service, which allows Internet users to log on to many different web sites using a single digital identity, single sign-on, eliminating the need for a different user name and password for each site. OpenID is a decentralized, free and open standard that lets users control the amount of personal information they provide.

An OpenID is in the form of a URL. This URL can be the domain name of your own website, or the URL of an OpenID Identity Provider. When you log in with an OpenID, you have to log in to the Identity Provider for validation.

Using OpenID-enabled sites, web users do not need to remember traditional items of identity such as username and password. Instead, they only need to be registered with any OpenID "identity provider" (IdP). Since OpenID is decentralized, any website can use OpenID as a way for users to sign in; OpenID does not require a centralized authority to confirm a user's digital identity.

OpenID is increasingly gaining adoption among large sites, with organizations like AOL, BBC, Google, IBM, Microsoft, MySpace, Orange, VeriSign, Yandex and Yahoo! acting as providers. In addition, OpenID can be used with Windows CardSpace.

2005

The original OpenID authentication protocol was developed in May 2005 by Brad Fitzpatrick, creator of popular community website LiveJournal, while working at Six Apart. OpenID support was soon implemented on LiveJournal and fellow LiveJournal engine community DeadJournal for blog post comments, and quickly gained attention in the digital identity community. Web developer JanRain was an early supporter of OpenID, providing OpenID software libraries and expanding its business around OpenID-based services.

In late June, discussions started between OpenID developers and developers from enterprise software company NetMesh, leading to collaboration on interoperability between OpenID and NetMesh's similar Light-Weight Identity (LID) protocol. The direct result of the collaboration was the Yadis discovery protocol, which was announced on October 24, 2005. After a discussion at the 2005 Internet Identity Workshop a few days later, XRI/i-names developers joined the Yadis project, contributing their Extensible Resource Descriptor Sequence (XRDS) format for utilization in the protocol.

In December, developers at Sxip Identity began discussions with the OpenID/Yadis community after announcing a shift in the development of version 2.0 of its Simple Extensible Identity Protocol (SXIP) to URL-based identities like in LID and OpenID.