Batman Day is an annual event organized by DC Entertainment to celebrate and promote Batman.
The first Batman Day was July 23, 2014. It was a date selected by DC Comics and Warner Bros. to celebrate Batman's 75th Anniversary. The day was chosen to coincide with San Diego Comic-Con 2014. Subsequent Batman Days have been on either the third or fourth Saturday in September.
The actual anniversary date of the first appearance of Batman in Detective Comics #27 is March 30, 1939. From Wikipedia
