This note summarises recent progress in the formulation of flavour mixing and oscillations in pseudo-Hermitian quantum theories with non-Hermitian mass mixing matrices. Such non-Hermitian quantum theories are made viable by the existence of a discrete anti-linear symmetry of the Hamiltonian, which ensures that states have real energies. We describe oscillation and survival probabilities in a non-Hermitian two-state quantum mechanical system that are consistent with unitarity, and highlight features of these pseudo-Hermitian flavour oscillations that are unique compared to their Hermitian counterparts.