From the Fantasy Flight Games website: The town of Arkham, Massachusetts, is in a panic. Horrific and bizarre events have begun to occur with increasing frequency—all seeming to point towards some cataclysmic event in the near future that may spell disaster for everyone. Only one small band of investigators can save Arkham from the Great Old Ones and destruction!
Arkham Horror is a purely cooperative game for 1-8 players ages 12 and up, and can be played in 2-4 hours
Starting in the summer of 2008, FFG began publishing scenarios as part of an open-invitation "Summer League" program. Players were invited to submit the results of their games using these scenarios, and results/standings were published to FFGs web site.