A66

A66, A 66 or A-66 may refer to:
 * A66 State Route (Australia), a road in South Australia connecting Keith and Port MacDonnell
 * A66 road (England), a road connecting Middlesbrough and Penrith/Workington
 * A66 motorway (France), a road connecting Villefranche-de-Lauragais and Pamiers
 * A66 motorway (Germany), a road connecting the Taunus and Fulda
 * A66 motorway (Spain), a road connecting Gijón and Seville
 * Benoni Defense, in the Encyclopaedia of Chess Openings
 * HLA-A66, an HLA-A serotype