C66

C66 or C-66 may refer to:
 * C-66 (Michigan county highway)
 * Berlin Defence (chess), a chess opening
 * Caldwell 66, a globular cluster
 * Caudron C.66, a French biplane
 * HMCS Uganda (C66), later renamed HMCS Quebec, a Fiji-class cruiser of the Royal Canadian Navy
 * Lockheed C-66 Lodestar, an American transport aircraft
 * Migration for Employment Convention, 1939 of the International Labour Organization
 * Siemens C66, a mobile phone