Book excerpt: The Internet Inter-ORB Protocol (IIOP) is a communications mechanism that allows object request brokers (ORBs) to communicate with one another. IIOP is an integral part of the broader Common Object Request Broker Architecture (CORBA) standard that has been developed and widely promoted throughout industry by the Object Management Group. IIOP was designed to allow disparate software components to communicate with one another, and it ensures interoperability on top of the most popular communications protocol in use today -- TCP/IP. While IIOP is a specialized subset of the broader CORBA specification, its popularity is increasing steadily. In fact, IIOP support has become one of the standard checkbox items that software vendors are adding to their product descriptions. This book provides a broad perspective of IIOP, allowing any CORBA developer to gain an in-depth understanding of this foundational standard. In turn, an increased knowledge of IIOP allows systems developers to more easily build interoperable objects for the enterprise.