The following highways are numbered 666:

Belgium

• The pilgrimage centre of Banneux in Belgium is located on the N666 road.

Canada

• Alberta Highway 666
• Ontario Highway 666 (former)

Ireland

• R666

Italy

• Strada regionale 666 di Sora (formerly strada statale 666 di Sora)

Philippines

• N666 highway (Philippines)

Sweden

• Länsväg 666, in Uppland, eastbound from Alunda.

United Kingdom

• A666 road

United States

• US 666 (former, renumbered in 2003 to US 491)
• SR 666
• MD 666 (former)
• SR 666
• PA 666
• PR-666
• FM 666