In an offical announces on Rockstar's home website which can be read here: http://www.rockstargames.com/newswire/article/48591/grand-theft-auto-v-is-coming-9172013.html
Rockstar Games announced the official release date for Grand Theft Auto V (GTA V)
"Today, we have an official release date to share with you: Grand Theft Auto V will arrive in stores on September 17, 2013."
In breaking tradition with Rockstar's traditional May release schedule the developer has moved the release date to September citing, "it simply needs a little more polish to be of the standard we and, more importantly, you require.".