||Scarcely any other technology engages the software industry these days like XML. Its simple structure and its extensibility have lead to a vast quantity of applications since its standardisation. Especially the booming E-business, has become XML’s main field of application. The growing importance of the World Wide Web for business also increased the interest in distributed systems. XML may be used as an operating-system-and-language-independent format for data exchange. Sometimes data exchange is not enough. In distributed applications, it is often necessary to invoke data processing on a remote machine. Since the object-oriented paradigm has taken the leadership in software development, this task is fulfilled by distributed object architectures, which provide Client/Server functionality with objects. The most common models are OMG CORBA and Microsoft COM/DCOM. A lightweight solution is Sun’s Java RMI. None of these organisations could establish their distribution model as a standard throughout the whole software industry. COM is just a standard within the Microsoft world and CORBA lacks acceptance from the Microsoft community, whilst Java RMI is tied to the Java programming language. XML on the other hand is a standard, which is accepted and supported by all major players in the software industry and not at least because of this fact, it is widely used. Now there is a chance to provide the software world with real interoperability. A number of XML-based interoperability approaches already exist, some of them are already rather mature. To serve as application glue is one more facet of XML, the forthcoming lingua franca of the World Wide Web. Firstly, this work briefly describes existing approaches of using XML as mediator in distributed applications, where we focus on solutions, which allow RPC-style communication. The nowadays most important one, which is the Simple Object Access Protocol (SOAP), is examined in detail. The second major part of this work demonstrates the applicability of such XML-based solutions in distributed applications. I present the SOAP Open Framework for Internet Applications (SOFIA), which realizes a prototype of a SOAP processor for RPC over the World Wide Web. Its architecture is characterized by a modular and extensible structure. The primarily intended target service providers are Enterprise JavaBeans application servers, but adapters to other services can easily be added.