The Citadel is an archive of information for George R.R. Martin's A Song of Ice and Fire.
New to the series? Read our spoiler-free review of A Game of Thrones.
The changes are very minor -- mostly a few typos we caught in time to correct for the US edition, after the British edition had already gone to press.
Also the US edition will have one map the UK edition lacks, and updated versions of the older maps.
The Westeros network consists of several different sites, including a forum and a wiki, for all your A Song of Ice and Fire needs.