Internet top-level domain

Two-letter top-level domains are assigned to countries and dependencies by ICANN according to ISO country codes list ([1]).

As of 9.09.2015 249 country codes are assigned.

13 ISO codes are exceptionally reserved at requests of countries and organisations:

AC Ascension Island
CP Clipperton Island
DG Diego Garcia
EA Ceuta and Melilla
EU European Union
EZ (European OTC derivatives)
FX France, Metropolitan
IC Canary Islands
SU USSR
TA Tristan da Cunha
UK United Kingdom
UN United Nations

Two reserved codes - EU and SU - are delegated as Internet TLDs. Domain UK is delegated instead of ISO code GB.

7 ISO codes are transitionally reserved for 50 years after renaming of territories or dissolution of federations:

BU Burma                 Reserved from 1989-12 to 2039-12. New country name: Myanmar                   MM
NT Neutral Zone          Reserved from 1993-07 to 2043-07. Divided between Iraq and Saudi Arabia     IQ+SA
ZR Zaire                 Reserved from 1997-07 to 2047-07. New country name: Congo (Kinshasa)          CD
TP East Timor            Reserved from 2002-05 to 2052-05. New country name: Timor-Leste               TL
YU Yugoslavia            Reserved from 2003-07 to 2053-07. New country name: Serbia and Montenegro     CS
CS Serbia and Montenegro Reserved from 2006-09 to 2056-09. Divided to Serbia and Montenegro          RS+ME
AN Netherlands Antilles  Reserved from 2010-12 to 2060-12. Divided (see below)                      BQ+CW+SX

.AN deleted by ISO on 2010-12-15/2011-12-13 - and is still transitionally reserved to Netherlands Antilles from 2010-12 to 2060-12 (divided into: Bonaire, Sint Eustatius and Saba - BQ - Curaçao - CW and Sint Maarten - SX).