Microsoft has recently released Consumer Preview build of it which is a kind of Beta version. There was also a trial version of MS Office 2013, If you had downloaded trail version of it then you can easily upgrade to full version.
MS Office 2013 comes with many new features like could integration, PDF editing, optimized for touch screen devices, and lot more.
Now Microsoft has announced that they are going to release it for General Public on 29 January 2013. Microsoft has uploaded a teaser page of MS Office 2013 which tells that GA will be on 29 January.