The representation of resources is what is sent back and forth between clients and servers in a RESTful system. A representation is a temporal state of the actual data located in a storage device at the time of request. In general terms, it is a binary stream, together with its metadata, which describes how the stream is to be consumed by the client. The metadata can also contain extra information about the resource, for example, validation, encryption information, or extra code to be executed at runtime.

Throughout the life of a web service, there may be a variety of clients requesting resources. Different clients can consume different representations of the same resource. Therefore, a representation can take various forms, such as an image, a text file, an XML, or a JSON format. However, all clients will use the same URI with appropriate Accept header values for accessing the same resource in different representations.

For the human-generated requests through a web browser, a representation is typically in the form of an HTML page. For automated requests from other web services, readability is not as important, and a more efficient representation, such as JSON or XML, can be used.