The R668 road is a regional road in Ireland from Lismore, County Waterford to Cahir in County Tipperary, through Clogheen and Ballylooby.

The Lismore–Clogheen section is a scenic route through the Vee Gap (Irish: Bóthar na gCorr[1]) in the Knockmealdown Mountains, between Sugarloaf Hill and Knockshanahullion.

[2] In the eighteenth century, the Cahir–Clogheen section was part of the main road from Cashel to Cork city.

[3] It was superseded in the early 19th century by the construction of what is now the R639 road between Cahir and Mitchelstown.

[4] At Glentanagree Bridge, the R669 forks off to the south east past Mount Melleray to Cappoquin.