Transition from IPv4 to IPv6 is one of the most crucial components of all the upcoming networks and communication facilities.The book emphasizes on eliminating the drawbacks of the available tunneling mechanisms and improvising their functionality in terms of security, efficiency and reliability. It highlights the reasons for IPv6 deployment, its advantages, different phases and scenarios of IPv6 transition and associated challenges. It provides a brief introduction of the available transition mechanisms that enable communication between IPv4 and IPv6 networks. It also includes comparative evaluation of the prominent tunneling mechanisms and provides a detailed discussion on possible security vulnerabilities in existing tunneling strategies. It proposes threat mitigation measures and a mechansim to improve scalability and efficiency of IPv6 transition scenario.