Interoperability between software components within an application is achieved through component models like CORBA, DCOM and JavaBeans. Here interoperability is achieved through the standardization of component interfaces or application programming interfaces (API’s). The classical example is OMG’s Object Management Architecture. Interfaces of CORBA components are defined with the Interface Definition Language (IDL) and interfaces of generic components are standardized by the OMG. Several approaches try to achieve interoperability of electronic commerce components. OMG’s Electronic Commerce Domain Task Force (ECDTF) tries to standardize interfaces of catalogs, brokers, agencies and other components for electronic markets. This should lead to a third party market of vendors for these electronic commerce components and to interoperability also between systems of different market participants. A good example is the Workflow framework, which specifies the API protocols between various components in a typical workflow system as defined by Workflow Management Coalition (WFMC). Another approach tries to achieve interoperability between electronic commerce applications through the standardization of documents and document exchanges. Some of the first approaches in this direction come from an Internet Engineering Task Force (IETF) workgroup covering EDI (EDIINT), which has recommended standards for secure, interoperable electronic data interchange over the Internet. Many new approaches use XML, the eXtensible Markup Language created and developed by the W3C XML Working Group, as an underlying basis. The language combines the simplicity of HTML with the computability of EDI Standards and is meant to make transaction sets easier to define and use across companies. XML-centric interoperability enables computer systems to exchange documents – invoices, loan applications, contracts, insurance claims, and so on, as Electronic Data Interchange has tried to achieve for many years. XML is intended for use on the World Wide Web and retains features such as vendor independence, user extensibility, complex structure,validation, and human readability. Microsoft and Netscape have promised to provide XML parsers in future generations of Web browsers, and other companies such as Veo Systems (Meltzer and Glushko, 1998), a spin-off of CommerceNet, are rushing to develop common business libraries built on XML. Compared to document-centric interoperability, API-oriented interoperability is difficult to achieve across various different application domains although it may work well in some application domains. However, realizing document-centric interoperability may require many years to mature as it takes time to unify the domain specific vocabulary and common business libraries.