Project Tango (also known as WSIT for Web Services Interoperability Technology), an integrated part of GlassFish V2, is an open source implementation of the key enterprise Web services technologies, commonly known as WS-*. The technologies are divided into three main areas: Security, Reliability, and Transactions. One of the main goals of Project Tango is to provide interoperability with Windows Communication Foundation, the Web services stack bundled with the .NET 3.0 platform. This article by Arun Gupta was written to offer a clear overview of Project Tango to show some details about its programming model and the ideas behind it so that you can decide whether you should use it for Web services, and how you can use it efficiently.