Windows Communication Foundation 101
Windows Communication Foundation (WCF) is Microsoft’s unified programming model for building service-oriented applications. It enables developers to build secure, reliable, transacted solutions that integrate across platforms and interoperate with existing investments. So you can expose a service over multiple channels, each of which can be configured to take advantage of select protocols like WS-Security, WS-Trust or WS-SecureConversation for secure message exchanges; WS-ReliableMessaging for reliable transfer of messages etc. You can also choose what transport protocol you want to use for communication (eg: HTTP, TCP, MSMQ, Named Pipes, custom) and the encoding format (XML, Binary, MTOM).
WCF is able to support interoperability as it’s native messaging protocol is SOAP (an open standard) thus providing the opportunity for WCF services to interact with different technologies running on Microsoft and non-Microsoft platforms. It also works with its predecessors like COM+ and Enterprise Services which reduces the amount of infrastructure code that you have to write as a developer in order to achieve heterogeneous interoperability. Here is a performance article you can go through.
Some resources to get started:
Understanding Windows Communication Foundation Virtual Lab
Books
Learning WCF: A Hands-on Guide
Inside Windows® Communication Foundation
Programming WCF Services by Juval Lowy (Author)