The Bethesda Blog announces that the Old World Blues DLC for Fallout New Vegas is now available through Steam. The announcement includes an extensive look at what this project represents written by Chris Avellone, and here's a bit from that:

There is an expression in the wasteland called “Old World Blues.” It refers to those obsessed with the past they can’t see the present, much less the future for what it is. Their eyes are like pilot lights, guttering and spent, the realities of their world continuing on around them as they stare into the past.

Old World Blues is built around the history of Fallout games we’ve worked on. It’s history-that’s-created-history, with a dash of what might have been from past games, media, and design documents from Fallout 1, 2, and past Fallout projects given new life. From Lobotomites, DNA splicing, Cazadores, Night Stalkers, where-the-hell-did-those-plants-in-the-Mojave-come-from, the scientific enclave of Big MT itself, Proton weapons, and giant robotic scorpions, all of these things formed the nucleus of taking a trip into the past-is-present Fallout universe to see a slice of the Old World that’s been fenced in and feeding on itself for far too long. We wanted you to see the context and homages to the Fallout universe in a scientific preserve, both from the distant Fallout past to more recent adventures in New Vegas and the DLCs. As you’ll discover, Big MT (or the Big “Empty”) is filled with what-might-have-been… and all that was lost that potentially could have made a better world for all. There’s an undercurrent of the blues all around Big MT… but if you’re strong enough, you can change it, and the whole meaning of Old World Blues forever.