Posted on Monday 28 October 2002 to Story So Far
From a nice FAQ found over at zompist.com
A language family is a group of languages that have been proven to have descended from a common ancestral language. Branches of families likewise represent groups of languages with a more recent common ancestor. For example, English, Dutch, and German have a common ancestor which we label Proto-West-Germanic, and thus belong to the West Germanic branch of Germanic. Icelandic and Norwegian are descended from Proto-North Germanic, a separate branch of Germanic. All the Germanic languages have a common ancestor, Proto-Germanic; farther back, this ancestor was descended from Proto-Indo-European, as were the ancestors of the Italic, Slavic, and other branches.
Not all languages are known to be related to each other. It is possible that they are related but the evidence of relationship has been lost; it's also possible they arose separately. It is likely that some of the families listed here will eventually turn out to be related to one another.
The Indo-European Family
Non-Indo-European Families
There are many New Guinean language families; some linguists group them all together as "Papuan" but this too is controversial. There are 26 families of Australian languages; the largest is Pama-Nyungan.