While the details of the next-generation IPv6 protocol are now reaching maturity, the next hurdle in realizing the promises of IPv6 is the need for deployment on a wider scale. Previously, the migration from IPv4 to IPv6 has been considered nontrivial, a factor generally attributed to thwarting its success. However, with the advent of a number of new transitioning techniques the evolution to IPv6 is now becoming increasingly feasible. These transitioning techniques offer tunneling and translation solutions that enable the gradual introduction of IPv6 support into an existing IPv4 infrastructure. Nevertheless, it is not yet clear what form this evolution is likely to take, which phases are likely to exist, and how the transition process will proceed. This article examines existing IETF IPv6 transitioning mechanisms and discusses the key issues involved in IPv6 deployment. We examine those aspects that potentially affect the choice of transition mechanisms and look at what factors are likely to mould the evolutionary path.