There are about forty five of them. Most of them are spoken in Alaska and northern North America, but some are spoken in areas as far south as Mexico.
They're about as different from each other as the Indo-European languages are: as different as English and Greek, for instance (though just as obviously historically connected). In fact, in some ways they're more different than English and Greek because some of the Athabaskan languages use tone (where the pitch of the voice makes a word mean different things) and some don't.
Several of the Athabaskan languages are terrifyingly close to extinction: Han and Holikachuk, for example, have recently each been down to only twelve speakers. Twelve!
One great problem with - or perhaps great glory of - the Athabaskan languages is that their grammar is very difficult because they're distinguished by an inconvenient habit of breaking their own rules. Personally, I admire this in a language.
Why do we owe them so much?
Well, the Athabaskan languages were used by the linguist Edward Sapir (1884 - 1939) as proof that culture isn't constructed by language (there were people arguing at the time that Europeans were best because they had the best language) because Athabaskan speakers belong to very different cultures.
It's been an important principle in supporting native languages throughout the world. It was important in showing the Europeans are best people to be ignorant and wrong, too.
So, yes: we all owe a lot to the speakers of Athabaskan.
Alaskan Athabaskans c 1851
Word To Consider Today: Athabaskan. This word is an anglicised version of the Cree name for Lake Athabasca in Canada, and means there are reeds one after another.