This was prompted by an M&S recruitment ad - could I honestly (in my terms) say I'm fluent - no. Would some other people say I speak fair Spanish? Yes. On top of that I find that despite the odd very good conversation I'm mostly frustrated that my Spanish won't keep up with the speed of my English brain..... For me, I think there's more to it than just being able to chit chat in the supermarket or chiringuito, I reckon being able to demonstrate the existence of the bit between the ears would help, & without that I certainly couldn't say I'm fluent.
How do you define fluency?

Well, since it requires an understanding of intonation and the subtley of timing it's delivery - not to say knowiing how words can have different meanings, I'd say the ability to tell jokes (more than just a "knock-knock" style one-liner) is a good indication.
Also the ability to swear, without hesitation, repitition or deviation for an extended period might impress some people

I find the ability to hold a really good argument complete with arm waving, pointing, foot stamping and face pulling not only displays a level of fluency, it wins a great deal of respect from the other party.

I tend to avoid anyone in a uniform or in posession of some kind of firearm, best left to the native speakers who have a better judge of intonation...

There are different levels of fluency (I suppose ranging from "defending oneself" to "dominating the language" is a loose translation of how the Spanish put it). You can have a basic level of fluency (understand what is normally said and be able to be understood by others), but you'll soon come a cropper in most jobs as there is normally jargon. For instance if you work with a computer you may know what teclado or arroba means, but would you know how to translate "update all rows where the foreign key exists in the orders table"? If you work in healthcare there would be a lot of other words and expressions you'd need to know (indeed you may not even know the meaning of certain words in your own language). And even the most fluent speakers can rarely pass for a local. It's not the same as being bi-lingual - which is normally only achieved if you've spent your childhood in a particular country.

I find it useful to learn certain expressions and idioms as they can often impress. For example if you're asked where your friend is today, instead of explaining "oh - he had too much to drink last night and now he has a resaca/hangover" you could say "esta con el mono". Of course the danger with this is your companion then starts using idioms a lot more and you quickly lose your way in the conversation.

I would say when the words flow constantly and effortlessly like a fluid,............
.......or like me after a few jars on a Saturday night.

Mind you, I doubt if anyone else would understand a single word!.......

For me fluency means that you do not have to do mental gymnastics in your mind before you speak.
You dont have to rehearse different ways of saying things, you just get it right the first time, and then you dont sit and think later, that you wish you would have said it better.
I know that I am fluent, because, if I watch a film and someone asks me what language it was in, most times I cant remember, because I am confortable with both languages.

I get one of those but not the other. I can't usually remember what language I watched or heard or read something in, but I do notice my mistakes and wish I'd said things better.

If you have to ask or even wonder if you are fluent, then like me, you are not. lol

i agree.

i don't think fluent means "perfect", but fluid, without thinking without stuttering and hesitating too much (no more than you would in English).

hence fluent/fluido, it flows

Nobody is perfect in any language.

Well you sound "nearly there" to me..........

I think that total fluency is only achieved if you think in the language.

Good point....I would agree,... though I think I probably still have a long way to go.

If you understand andaluz, you´re fluent.