My personal take on free will is that it’s an illusion, as is consciousness.
The impression of free-will is very believable though as the brain probably exhibits chaotic dynamics. From any given state the brain is in, a slight change, however minute, could give rise to a very different outcome later on. This means that for any system with a model that’s external to an individual brain (e.g. a brain simulation if such a thing is possible), it is impossible for that model to completely predict the behaviour of the brain… eventually the brain’s state will diverge from the model. The important point is, this can happen even if the brain is completely deterministic. So even if the rules governing our cognition are unwavering instructions, which I think is unlikely, there is still the inability for a system outside of the brain to predict it’s behaviour.
In addition, I believe that consciousness is due to a recursive model that represents ourselves (ala Douglas Hofstadter’s book – I am a Strange Loop). As this is a model of the epiphenomenon of our “self”, it also has incomplete knowledge of the rest of the brain – this gives our conscious minds the illusion of free will as it can’t completely predict what it/we will do next. We think we are weighing up choices based on our knowledge and then making a “decision”, but that’s because we (our conscious minds) don’t have complete knowledge of the brain’s underlying hardware which ultimately leads us to that choice. This lack of knowledge in our conscious minds is what we call “free will”.
 Or at least I’d expect it to, I don’t have references I’ve read over, but this looks promising.
 That is, assuming we exclude the almost impossible ideal of having perfect knowledge of the brain’s state which would include all neurochemistry as well as structure.
This post is taken from a comment I made to Leo Parker Dirac’s post on “Free Will and Turing-completeness of the Brain”. Turns out I think it’s a relatively succinct description of what the concept of free will actually is so I thought I’d repost it here…