The document provides an overview of network virtualization. It defines network virtualization as isolating computational and network resources through virtualization to allocate them to logical virtual networks. It discusses key features such as segmentation, isolation, and encapsulation. It also describes several network virtualization architectures including ISONI, VNET, and CABO. It then reviews some proof of concept implementations on testbeds like HEN and PlanetLab. Finally, it provides references for further reading on network virtualization.