  In this talk, we present the results of the complete one-loop matching of the
seesaw model onto its low-energy effective theory by integrating out three
right-handed neutrinos at the one-loop level. We find that there are 31
independent dimension-6 (dim-6) operators (barring flavor structures and
Hermitian conjugates) in the Warsaw basis, and the standard-model couplings and
the Wilson coefficient of the Weinberg operator acquire threshold corrections
at the one-loop level. The complete Lagrangian up to dim-6 at the one-loop
level is derived, which is indispensable for consistent explorations of the
impact of heavy right-handed neutrinos at low energies.
