A uniform resource identifier is a kind of name used to uniquely refer to individual resources at a global level — such that a given resource in the entire world could not be confused for another. URIs take the form of a scheme (e.g. http:) connected to a name. The purpose of the scheme is to denote the kind of communication channel, if any, to which the URI is relevant. The name that follows is dependent on the scheme, and ought to be descriptive enough to uniquely identify the resource, or be relative to some existing context.

One type of URI is the uniform resource locator, which is similar to (and was modeled after) file names with the addition of an authority section to allow the universal location and retrieval of a given resource in a process known as dereferencing. URLs are by far the most common type of URI, like those found the location bar of Web browser.

The URI is a generalization of the URL, which was initially invented to support HTTP. Another type of URI is the uniform resource name, which identifies objects that are not network resources. A prime example of a URN is the ISBN namespace, e.g. urn:isbn:978-0123740373.

As resources have many names, it is possible for many URIs to point to a single resource.