X-Day

X-Day may refer to:


 * X-Day (Church of the SubGenius), a festival associated with the Church of the SubGenius
 * X-Day (manga), a 2002 manga written by Setona Mizushiro
 * March 20, 2003 anti-war protest, a protests against the Iraq War
 * The first day of Operation Downfall, the planned Allied invasion of Japan during World War II
 * X Day (musical), a musical by Akinori Nakagawa