What were the geological relations between Calabria and Sardinia before the opening of the Tyrrhenian Sea? It would be premature to reach a definitive conclusion, so we consider (without reaching any conclusions) four major open questions that bear on the original geologic relationships between Sardinia and Calabria, and that are closely interconnected: (1) Was Calabria a single terrane during post-Hercynian time (Mesozoic and Cenozoic), or is it a composite terrane formed by Cenozoic collision of two subterranes, northern and southern? (2) What has the history of subduction under Calabria been? One interpretation envisions an early «Alpine», east-dipping subduction followed by a later «Apennine», west-dipping subduction; an alternative view is that only west-dipping subduction has occurred. (3) Is there a recognizable match between the Hercynian and Mesozoic geology of Sardinia and of Calabria? The Hercynian evolution of Sardinia is now generally understood, although with some open questions. That of Calabria is still poorly known, which makes it hard at this point to use a match of the Hercynian patterns to constrain a pre-Tyrrhenian terrane reconstruction, but the character of Mesozoic carbonate sequences may provide an additional constraint. (4) How was Calabria extended during its rifting away from Sardinia?