The message standards define the structure of the communication units and the ways they can be exchanged between services.

The elementary message concepts are: message, operation, interface, interface binding, endpoint and service. A message is the basic unit of communication between a client and a web service. An operation is the sequence of actions related to a single service invocation. An interface is a logical grouping of operations. An interface binding relates an abstract interface to a specific transport protocol and message format. An endpoint is the location of a bound interface, specified by an URI (Uniform Resource Identifier). Finally, the service is a collection of endpoints.

SOAP defines the message protocol for Web Services as a XML document, making transport independence possible. The SOAP envelope separates the header with system data from the body with application data or fault information. The header can contain data from different Web Service extension protocols.

MTOM/XOP is used to transport binary data in SOAP messages, replacing former approaches like SwA and WS-Attachments/DIME. XOP is a data encoding that allows both binary data and text data in XML documents, without using base 64 encoding. MTOM specifies how to use XOP in SOAP messages.

WS-Addressing allows for the addressing and forwarding of SOAP messages in a transport-independent way. WS-Addressing defines header elements to identify the message, the SOAP nodes and the action to perform. The addressing with endpoint references is more fine-grained than with basic URIs, allowing for properties and additional parameters.

WS-Enumeration enables the creation of data enumeration sessions encompassing several requests and responses.

WS-Eventing and WS-Notification are competing standards for asynchronous event notification using Web Services. With either one, polling is not necessary. Both models have subscribers, subscription managers and event consumers.

WS-Polling specifies mechanisms for successive requests when asynchronous notifications are made impossible by a firewall or another reason. In these cases, one of the endpoints must periodically connect to check for information updates.