.NET Web Services help you write components whose methods can be invoked across the Internet using any .NET programming language. Developers who are creating web services can build one upon another, taking advantage of the connectivity that is at the heart of the Web. Adding value takes precedence over reinventing the wheel.
The list of web services that might be useful to developers and end users seems boundless. A bookstore might provide a web service that takes an ISBN and returns the price and availability of a title. A hotel's web service might take a date range and number of guests and return a reservation. Another web service might take a telephone number and return a name and address. Yet another might provide information about the weather or shuttle launches.
Microsoft has announced a number of commercial .NET services as part of its .NET My Services initiative. Among these are its Passport service for identifying and authenticating users (see http://www.passport.com), as well as services for managing storage, notification, appointments, and a host of other applications. These services, as well as the ones you write, can be integrated with your applications just like any other business object.
In such a world, a single application might draw on and stitch together the services of hundreds of small web services distributed all over the world. This takes the Web to an entirely new dimension: not only is information retrieved and exchanged, but also methods are invoked and applications are executed.