To obtain Italian citizenship by descent through a grandparent, you need to meet the following criteria ^{1 2 3 4 5}:

1. Your grandfather must have been born in Italy and been an Italian citizen when your parent was born.
2. Your parent must not have renounced their right to Italian citizenship.
3. You may need to provide documentation proving the lineage and continuity of Italian citizenship.
4. Any living intermediate ascendant (e.g. parent or grandparent) will need to sign a declaration stating they never renounced their Italian citizenship.