Fallout 3 seems to be a big success. They put a lot on the line for this, and it (thankfully) paid off. Sales seem to be doing well and the reviews continue to come in very favorably.

So have they said anything about starting on Fallout 4 yet? Are they focusing on the downloadable content only right now? Are they just taking a break for the most part and then will start on 4?

Fallout 3 was a great success but I do think they are focusing on the upcoming DLC's. If they do make a FO4 then it would be a while.

LOL. It's only been three months since the release of Fallout 3. They're working on DLCs now, and it may be one or two years before Fallout 4.

TES:V, then Fallout 3.
There's no way in hell that FO4 will come out before TES:V.

Actually, one guy from Bethesda said there would be a F4 in some years, after TES5, and threw in a release year but, after that, another guy from Bethesda said it could be sooner.
So, at least, we know there will be a F4 and we know that, right now, they're working on TES5. I think the question is rather whether they will start F4 before they finish TES5.
If Bethesda starts hiring more people, we'll get some answer.

Bethesda got the rights for Fallout 3-5, or something. So yes, you can expect to see Fallout 4.

They originally got the rights for 3-5. But then in 2007 they bought the rights for the series.

I believe Fallout Online will come before FO4

I hope they'll be at least a couple of full expansions for F3 before they lay it to rest. I think Oblivion got laid to rest way too soon with only one little addon and one expansion.

Well yes, I knew they had full rights now to the Fallout series. So I knew already that they would MAKE a Fallout 4. I was just curious if they have maybe started to lay the groundwork for a Fallout 4 yet (read or heard anything). I can see them focusing on DLC and/or an expansion (or three) for Fallout 3 before putting it to rest. I just wish they had enough to work on TES V and Fallout 4 at the same time. Is Bethesda working on a Fallout Online?

Interplay is, the original developer of Fallout, I believe the DLCs will be the first thing that Bethesda finishes, their success will determine the healthiness and future of the series itself, however, unlike what others have said. There is at least one critic out there who speculated the return on Fallout 3, those actually taking their games back to the stores after two or three days, was much higher than sales as well as scores for the game have been highly inflated, according to his same opinion, due to fears felt from the overall gaming community. So, time will tell.