  This report constitutes the roadmap document prepared by the Double Beta
Decay APPEC Committee for the APPEC SAC on the future neutrinoless double beta
decay experimental programme in Europe. It reviews the existing, planned and
proposed technologies for neutrinoless double beta decay, their discovery
potential and technical challenges, making a critical examination of resources
and schedules. It also provides a concise discussion of the theoretical issues
and of the status and uncertainties on the nuclear matrix element evaluation.
