  In this talk, we present a recent investigation of the sufficient and
necessary conditions for CP conservation in the leptonic sector with massive
Majorana neutrinos in terms of CP-odd weak-basis invariants. The number of
weak-basis invariants to guarantee CP conservation in the leptonic sector is
clarified and a new set of invariants are advocated for the description of CP
conservation, given the physical parameters in their experimentally allowed
regions.
