What's up?

[Daruma]

Hi

What do you usually respond when somebody asks you, "What's up?"

[tzfujimino]

Hi

What do you usually respond when somebody asks you, "What's up?"

Hi, Daruma.

"Well, it's the opposite of down", I'd respond.

No, I'm only joking. I think it really depends on the context.

I'm also interested in this topic.

[Soup]

Hi

What do you usually respond when somebody asks you, "What's up?"

It's another way of asking "How are you?"

Q: What's up?
A: Nothing much, and you?

[colloquium]

It's another way of asking "How are you?"

Q: What's up?
A: Nothing much, and you?

But in the UK (unlike in the U.S), "what's up" is more likely to mean "what's the matter?".

It's something you might say to someone if you think they have a problem or are upset.

[beascarpetta]

It would depend on the situation , I'd say.

This phrase has replaced "Hello" or "Hi" as the most popular form of casual greeting.

it is also used to ask someone what the problem is as in "What are you doing?", "How are you?", "What is happening?" or "What gives?"

for possible answers have a look there

[Daruma]

- Nothing much.
- Nothing special.
- Not much.

Are these the most common responses to "What's up?"

[Offroad]

what's up?
What's up!
Nothing much! Everything's fine!

some may pronounce it "s'up"

hey, s'up?
nothing much!

Also...

What's up with this hair? why did you paint it green?
What's up with this panties? ...
What's up with this man?

[PROESL]

Hi

What do you usually respond when somebody asks you, "What's up?"

1. Not much. What's up with you?
2. Hey.
3. Hi.
4. Oh, not too much.
5. Not a whole lot.
6. Hey, what's up?
7. Not too much. Just takin' care of business.
8. Not a whole lot. Same old stuff. You know.

If you know the person well, you could say a little more.

1. Not too much. Whatchyyou been up to?
2. Not too much. How're things goin'?
3. Hey, what's up? How was your weekend?
4. Hey, how's it goin'? Ya wanna cup 'a coffee?
5. Not much, man. How you doin'?
6. Hey, I was jus' thinkin' about gettin' lunch. Jyou eat yet?

I'm going to save these. I know someone who could use some practice with this kind of stuff.

[PROESL]

- Nothing much.
- Nothing special.
- Not much.

Are these the most common responses to "What's up?"

I wouldn't say "nothing special" as a reply to "what's up", no. The other two are good and common.

You could say "nothing special" as a reply to "what's new".