Batman began publication in the Spring of 1940 and was published until 2011. Batman was initially released as a quarterly magazine, but changed to a bi-monthly format with issue #6. Beginning in 1954, National Periodical Publications began publishing eight issues of Batman a year. It wasn't until issue #260 that DC Comics began publishing Batman on a monthly basis, where it has remained ever since.
The first seven Batman Annual editions were actually released on a semi-annual basis, rather than yearly. They were double-sized issues reprinting classic Batman tales. With Annual #8, the series began publishing original stories. With the exception of Action Comics and Batman's own predecessor, Detective Comics, the Batman title remained one of the longest running DC comic book series of all time.