Inception

Theory
The entire plot was carefully orchestrated therapy for Cobb.  This theory makes no judgement as to if Cobb is still dreaming at the end, or if the "reality" scenes were in fact reality or just another dream level.  It could just as easily be understood as one or the other.

Having said that: Based on the specific circumstances of the end, mainly the children being in the exact same clothes, age, situation, etc as his "visions" throughout the movie, the evidence would indeed suggest that he is still stuck.

The main point of this interpretation was that almost all of the other characters involved - Saito, Ariadne, etc, were all real.  But not only were they real, they were expressly interested in helping Cobb work through his issues by orchestrating a "double blind" scenario surrounding Fisher so that Cobb would not be aware of their intent.

Evidence
1) Saito just so happens to get involved with Cobb and Arthur in a job-gone-bad situation in which he flips the script on Cobb and, in turn, "hires" him in a corporate take over. You would think, that for such a typical situation, there are thousands of less extravagant ways of going about it, and yet here is a situation that *just so happens* to trigger Cobb into offering the solution of Inception, and just so happens to know exactly what to offer him: A chance to get back to his children. In psychological spaces, this is called "priming".

2) Once involved, Saito insists that he come along with, citing a desire to "ensure that the task is completed". Logically this makes no sense. Assuming all of the characters are self motivated for a moment, just because Saito has been trained to protect his mind from invasion, doesn't automatically give him the ability to actively participate in shared dreaming and all of the assisting he signed himself up for. The actual professionals (Cobb, Arthur) wouldn't have agreed to bring him in being such a liability. And certainly, even if they initially agreed to do so, once the plan evolved into having to go 3 dreams deep, there should have been immediate concern that Saito, or several other characters, wouldn't have been able to handle it.

Furthermore, the perceived time-pressure created by the flight to LAX is also un-necessary. Cobb's motivation is to return to his children who live in a specifically peaceful place and in a specifically peaceful society. He's not "escaping" to the US to live on the run, his aim is to return to a repaired family situation. Saito could have just as easily "made the call" to clear him at LAX, not gotten involved in the risks of entering the dream, and threatened Cobb with the idea of making *another* call to re-ruin his standing should Fisher  fail to break up the corporation.  Easy, simple, self-motivated.

Saito instead insists on going with. This tells me that he is a plant, and essentially represents the promise of hope. His agreement with Cobb, his entire purpose, is to remind Cobb of the "one last job" that sets everything straight if it goes well.  This gives Cobb an "eye on the prize" perspective.

3) Cobb needs an architect for the program. He visits Miles, who just so happens to have the perfect student for the job - Ariadne.  Miles also makes sure to "prime" Cobb with the idea that she is *better* than Cobb could imagine. This is a psychological disarming technique because Cobb, being an excellent architect himself, would not be able to accept (or to his perspective, work with) a person of perceived inferior ability.

Ariadne plays the roll perfectly - starting off as only mildly put off by the fact that she was being asked to participate in something highly illegal, morally questionable, and extremely risky.  However, she just so happens to become extremely involved not only as an architect for the job, but personally with Cobb to help "uncover" his repressed issues with Mal - even through Cobb already has a friend figure (Arthur) who is aware of the Mal situation and could be offering more direct support.

The point here is that if Saito represents the goal, the promise of correction, then Ariadne represents the guiding hand of therapy through the obstacle. She is there to ensure Cobb confronts Mal in his subconscious.

This is also why Ariadne is with him for almost all of the scenes involving Mal. This is why, instead of being terrified of his "elevator of horrors" (aka compartmentalization), she takes the risk of forcing herself down into the Basement - she was analyzing him, forcing herself into the full extent of what Cobb had created, closing the distance of Cobb's willingness to work with her.

Finally, Ariadne is a figure in Greek Mythology who helped Theseus overcome the Minotar and escape the Labyrinth. This is essentially the similar role she plays for Cobb - except the Minotar is the angry shade-reflection of his wife.

4) When it is apparent that Fisher has mental security (dream stage 1), Cobbs is livid with Arthur for not realizing this. Arthur is perceived to be incompetent in this regard, however you get a different impression of this later when he is charged with guarding over the team in the hotel (dream stage 2) and figuring out a way to "kick" them without gravity. In that dream, he was operating in almost Matrix Agent like precision, kicking the shit out of bad guys in 3 dimensional space, protecting everyone, and devising a brilliant way to synchronize it all to the sound of music and wired explosives.

This tells me that he and everyone involved very likely knew that Fisher did have protection, but Cobb couldn't know until everyone was already committed to the plan, or he would have done things differently (or not at all, as he explains that they are "not at all prepared for this" in the garage escape scene).  It was necessary for the therapy to provide circumstances that were not easily escapable.

4) At the end, during the turbulent scene where Cobb is negotiating with Mal over Fisher, Ariadne is supervising the most crucial part of the entire session - ensuring the resolve between he and his subconscious - when this becomes apparent to Mal, it turns into the same "revolt against the subconscious" they explained with Fisher being tricked into becoming paranoid of his own guardians. Mal's reaction is to attack Cobb, which would have resulted in a violent, undesirable resolution (and pre-mature wake-up), so Ariadne shoots Mal, neutralizing that threat.  Now here is the second crucial point: After resolving such a deep seeded, psychologically draining situation, the question becomes "What now?". Cobbs may have resolved things with Mal, but that doesn't necessarily mean he has anything left to live for in that moment of loss and despair.

5) Which brings us full circle to Saito, and the promise of returning to his children. With Mal "taken care of", Ariadne reminds Cobb of the dire situation with Fisher and the fact that they need to go. When he says that he is staying behind, Ariadne is concerned until she confirms that he is staying behind to locate Saito.

At this point Ariadne's role is complete - which is why she allows herself to dive off the building of her own free will.  In other movies, having already come that far with the protagonist, through so many trials and tribulations, the classic response would have been for her to refuse to leave, to stay with him even if it means her doom, in which cases the protagonist usually has to force the issue - i.e. Cobb would have *pushed* her off the building when she refused - but this was not the case.

6) Which brings us to the close of the movie, where Cobbs washes up on the shore of his limbo again. only this time, there just so happens to be a patrolling sentry who finds him.  And this armed escort just so happens to lead Cobbs to the whereabouts of Saito, who just so happens to have a cozy little place nearby, even though limbo is described (by Arthur I believe) as this vast, infinite, unconstructed space.

I'm slightly torn here. I think the idea of Saito surviving the entire story unscathed would have been plenty to ensure Cobb has motivation to continue. Instead, he got shot, which appeared to be a genuine, unforeseen circumstance. When he died, and got stuck in limbo, it may very well be that the entire visit was a deliberate rescue attempt by Cobb, and not really part of the "overall plan". He still believed he needed Saito to get to his children so he did what he needed to do - thus I don't believe it was directly part of the "Mal Therapy".

Putting it all together:

How do you hypnotize a master hypnotist? How do you con the con man? How do you "fix" the broken psyche of a person who's primary job it was to manipulate the minds of people as his professional career?

By making him believe that he was being asked to do nothing more than his job one last time.

By offering him an immutable desire to repair his broken past, and finally, by allowing him to orchestrate an entire plan around Fisher, a plant, who had to have his own psychological issues to work out between he and his father, or it wouldn't have been believable.

You have to make Cobb believe that the central focus isn't on him through preoccupation. It has to be his idea to accept the job, his convincing the team he assembled to help, (many of which only offered a few brief moments of objection to the absurdity of it all). He needed a guide, an architect better than him to help him through the confrontation of Mal - but most importantly, he needed the bargain with honorable Saito to give him a concrete reminder that he had something tangible, his children, to return to once it was all said and done.

In Short: Inception appears to be a movie about a man who has Inception performed on him, unknowingly- by preoccupying him with the task of performing Inception on someone else, to repair the repressed guilt of consequences that resulted from doing the same to his wife.

So who's in on it? 
I believe that Fisher and Cobb are the only two people who didn't know the whole story. I believe Fisher did have real father issues, but that this was merely used as a believable stage for setting Cobb up. This is why people like Eames are genuinely interested in Fisher's outcome when he gets unexpectedly shot by Mal.

Mal offered a genuine wild card in the entire situation that the other characters did have to react to and work around. I don't think it was "planned" that Mal would incapacitate Fisher like she did, so those situations at least were improvised.

Were they all in on it because they were really figments of his imagination?
This is the interesting stance taken by some people I've discussed the movie with.  The basic premise was that Cobb created everyone - Arthur, Fisher, etc, artificially - that it is a sort of twisted self-therapy where helpful aspects of his subconscious manifested to help him fend off negative aspects of his subconscious and that he was the only "real" one at all.

The problem I have with this is twofold:

1) People who are crazy don't know they are crazy until they are presented with external evaluation that says they are crazy. So right off the bat, it seems a bit of a stretch that his mind could go through so much strange and grandiose effort to self regulate by creating this elaborate story for himself and just working it out on his own. Most therapists, doctors or psychologists don't even diagnose/treat themselves, it usually requires the aid of others especially when the trouble is serious.

2) There are too many situations happening in parallel that have literally nothing to do with Cobb and seemingly happen without even so much as a psychological consequence if they are all aspects of him.  My prime example is when Arthur and Ariadne are sitting in the lobby of Fisher's building, and Fisher's subconscious bodyguards are starting to get suspicious of them, so Arthur "tricks" Ariadne into kissing him as a distraction, which fails. "It was worth a try", he jokes.

Think about that scene for a moment and try to reconcile all of it as being all in his head. In the same instant, "real Cobb" is actually somewhere completely different, negotiating with Fisher himself and trying to trick him into trusting him.  So now, not only is his mind multitasking on an absurd number of levels and motivations now, but different aspects of him are making flirtatious plays on other aspects of him in the heat of danger? If so, call this movie "Sybil" and stick a fork in it, it's done.

The kiss scene is just one of many aspects of things that happen with, to me, obvious proof of individual, independent thought and intent that could only come from those people being real, bona-fide participants.

Which leads me to the final question:

Was this ALL a dream? AKA did his wife make it out, or was she crazy?


This is where my theory is altruistic. I will answer this question by following a pattern of logic and motivation.

Lets follow the logic path that says the "reality" they came back to was still a dream and his wife actually liberated herself from that second dream, pleading that Cobb do the same.  Mal, upon waking up to the real real world, would very quickly realize that her effort failed when Cobb does not wake up.   Now ask yourself: What would you do.

She is obviously somewhat trained in all this dream stuff. It's somewhat unclear if she was a "pro" like Cobb, but at the very least, she understood how things worked. So my first inclination would be to wake my husband the fuck up. Remember: The only reason the whole Limbo thing was a concern during the main story line was because they were in a chemically induced sleep which is harder to wake up from through normal kill-yourself means. I get the impression that this was not the case for Mal and Cobbs. They were merely staying in the dream world too long by choice.

So, wake him the fuck up. Throw him in a tub of cold water. Take him to the Log Ride at the local water park. And if she doesn't have this capacity, she could ask his father, who is like the Dumbledore of the entire story.

Hop back into his dream and shoot him in the head. Hop by back in his dream and simply reason with him on multiple levels: Show up- tell him it's not real, and if you get kicked out, show up again and tell him it's not real again. Involve other people.  Do you see where I'm going with this?

If everyone else, mainly his wife,  is "out there somewhere" just watching him lie in a hospital like an idiot while he dreams up the entire rest of the movie, then the entire story is a sham.

It is more believable to assume that IF his wife made it out, and basic attempts (prior to the contents of this movie) were futile in waking him up because he has fortified his mind to stay in the dream world, then my theory fits perfectly: They had to come up with an alternate, indirect way to help him resolve his issues by distracting him.

The problem here is that all versions of his wife in the Fisher arc are clearly figments, not the real deal. It seems unlikely that they would have left her completely out of helping, unless they felt that her presence would have caused a conflict with his versions.

It is more believable still that this is a story of a man who has locked himself in his mind because of the real loss of his wife.  He disassociated and created a series of compartments (elevator) to cope, figuring that he could work through things on his own and, slowly but surely, make his way down and confront Mal himself. But he was failing. Amidst trying to work through it all, he was starting to waiver on his resolve because he also wanted to preserve this memory of his wife where in the real world she was gone. As a result, his ability to keep his grips with reality in his jobs began to suffer, and it was clear to his friends and family that he was not pulling through as he should be.

Thus it is logical that his friend (Arthur) and his father (Miles) would have pooled their resources together to help him out by employing the same methods they were already well-versed in.

What about the final scene?

The facts are pretty hard to avoid. The children seemingly haven't aged. Everyone is wearing the same damn clothes.  The only thing that's different is the kids actually turn to face him and he spins the top on the table which, in all truth, actually appears to lose momentum right at the end, implying that it would fall over. Previously, all instances of the top "spinning forever" were clear and unwavering.

Anyhow, this scene indicates one of two logical conclusions:

1. He's still in a dream.
2. He is not in a dream, but not much time could have passed.

If he's still in a dream, then my theory would say that he still has things to accomplish before he's ready to wake up.  As with traditional therapy, you don't really try to resolve ALL of a person's issues at the same time, you typically dig to the deepest one (in this case his relationship with Mal) and then once you resolve the those, you can move on to solving other problems. So it wouldn't surprise me to learn that even though he has successfully gotten over Mal, he's still locked away holding on to his kids, which is another story entirely.

If he is NOT in a dream, then my theory would say that we are observing the affects of time-compression expressed through the dreams. It could very well be that when the mysterious agent that came to his house with the plane ticket (The "It's now or never" guy) that he was in fact being led into the plan plan that was prepared ahead of time. 

For all we know, he could have gotten into the cab with the fellow, drugged, brought back into his house, and laid back into his own bed, all the while the kids are outside playing with grandma.  

Then you take him into a dream where he believes he has fled the country, several other dreams where he believes he is passing the time as a dream secret agent, and then kick the whole plan off by introducing Saito's initial story.  

At final resolution, he wakes up, groggy, and stumbles out into the kitchen to find his kids, sill playing outside peacefully - and we're all left believing that it all happened in a space longer than 148 minutes.