M-Day

M-Day may refer to:


 * M-Day (book) (Russian: День „М”), a history book by Viktor Suvorov
 * M-Day, in the Marvel Comics Decimation storyline
 * M-Day, a military designation of days and hours for the day on which mobilization commences
 * Mobilization Day, the day Canadian police would arrest suspected communists under the secret PROFUNC program