Indo-European is a language family containing the CelticLanguage, IndicLanguage, GermanicLanguage, RomanceLanguage, SlavicLanguage, and GreekLanguage (among other) subfamilies.
The same tree is on http://www.wikipedia.com/wiki/IndoEuropean, for anyone interested, but more complete. The best IE language resource is http://www.geocities.com/indoeurop/