52 was a 52-part limited series, published weekly for one year, chronicling the events that take place during the missing year after the end of Infinite Crisis. None of the DC "Big Three" (Batman, Superman, Wonder Woman) are featured in costume in the pages of 52.
While DC had used the weekly format before, (most notably with Action Comics in April 1988), 52 was their first attempt to launch a new title as a weekly. Set in the time between the end of "Infinite Crisis" and the "One Year Later" story lines, 52 dealt with the events of the missing year - a year without Superman, Batman and Wonder Woman, The title was masterminded by writers Geoff Johns, Grant Morrison, Greg Rucka and Mark Waid, with Keith Giffen producing art breakdowns. Its weekly publication meant several artists had to handle the art, starting with Joe Bennett on the first four issues. A massive saga, spanning the whole DC Universe (and beyond), 52 introduced several new heroes and villains, including a new Question and Batwoman, before the big reveal of a new multiverse of fifty two realities, each containing an alternate Earth.
The story had a huge impact on the DC Universe, affecting everything from Black Adam's World War III spin off, to Booster Gold's post - 52 reality - spanning adventures. It also led into countdown to final crisis and left the DC Universe a dramatically different place.
Note: Indicias differ from the cover dates usually by 2 months (example: issue #1 is cover dated May 10, 2006, but the indicia indicates a July 2006 date).