Millions of novel examples of compact G2 holonomy manifolds
have been given in recent years as twisted connected sums of
asymptotically cylindrical Calabi-Yau threefolds. For compactifications
of type II string theories on such G2 manifolds, we give a construction
of their mirrors. Similar to Batyrev's construction of Calabi-Yau
mirrors, pairs of polytopes play a crucial role.