What are the Palantíri in J.R.R. Tolkien’s legendarium?

The Palantíri in J.R.R. Tolkien’s legendarium are seeing-stones.

These powerful crystal spheres allow communication and the observation of distant places. In The Lord of the Rings, important stones are kept at Orthanc, Minas Tirith, and elsewhere. They were made by the Noldor in the First Age and later brought to Middle-earth by Elendil and his sons.

The Palantír of Orthanc becomes especially important when Pippin looks into it. Sauron uses the stone to influence what can be seen and to extract information. Denethor also uses the stone of Minas Tirith, and his visions contribute to his despair because he sees the strength of Sauron but not the full possibility of resistance.

The stones are not ordinary crystal balls and do not grant unlimited knowledge. Their usefulness depends on the user, the stone involved, and the power of another will controlling or contesting the vision.