  This article describes a new experimental method for accelerator based
neutrino experiments called neutrino tagging. The method consists in exploiting
the neutrino production mechanism, the $\pi^{\pm}\to\mu^{\pm}\nu_\mu$ decay, to
kinematically reconstruct the neutrino properties from the decay incoming and
outgoing charged particles. The reconstruction of these particles relies on the
recent progress and on-going developments in silicon particle detector
technology. A detailed description of the method and achievable key
performances is presented, together with its potential benefits for short and
long baseline experiments. Then, a novel configuration for long baseline
experiments is discussed in which a tagged beam would be employed together with
mega-ton scale natural deep water Cherenkov detectors. The coarseness of this
type of detectors is overcome by the precision of the tagging and, conversely,
the rate limitation imposed by the tagging is outweighed by the virtually
unlimited size of the detector. These mutual benefits result in an affordable
design for next generations of long based line experiments. The physics
potential of such experiments is quantified using the Protvino to KM3NeT/ORCA
setup as a case study for which an unprecedented sensitivity to the leptonic CP
violation could be achieved.
