Free Will is the idea held by much of humanity which states that humans are in control of our own actions and determine our own destinies. However, there is actually no evidence beyond personal experience that humans have free will at all. We like to assume that we do, and it is fairly impractical and even potentially mentally unhealthy to do otherwise, but there is no definitive proof one way or the other. It is possible that we are all simply organic automatons, at the mercy of the chemical and physical reactions occuring in our own bodies and in the rest of the universe; quantum mechanics predicts that our tangible, observable universe is merely part of an infinite series of parallel realities, in which an infinite number of outcomes occurs, so what initially appears to be free will could just be the outcome meant to result in one particular reality (a "roll of the cosmic dice", as some scientists put it); or, as some exotic theories predict, our entire universe could simply be a giant simulation comparable to a computer game, in which case, humanity not only does not have free will, but we don't even technically exist.
Assuming that humans do have free will (as most do), this calls into question several aspects of God. For instance, God is said to have Omniscience, which means that he knows, and has always known, everything that will ever occur in the Universe's history. Leaving aside the paradoxical nature of Omnisciene for a moment, this assertion has dire connotations for the idea of free will. If God is nothing more than an observer (as in Deism), free will could technically exist in practice, but the very definition of free will calls for people to determine their own destinies, and under this model, God would know your destiny before you did, meaning that you never really "determined" anything. If God were more than just an observer (as most every sect outside of Deism proclaims), free will then becomes a meaningless concept- if God both knows your destiny and is capable of altering it to suit his purposes, you are not free, you are merely a slave under a very relaxed regime (which is oftentimes not so relaxed). So, for free will to truly exist, God cannot, or at the very least can be neither omniscient nor omnipotent; for a manageble facsimile of free will to exist, God must not be omnipotent; thus, under the traditional concept of God, humanity is incapable of truly having free will.
Ultimately, it is best to behave as if free will is a real phenomenon, but this forces us to question what limits, if any, free will has. Do animals- many of which behave on instinct- have free will? What about the potential robots of the future, or even the current ones which exist now? And indeed, some experimentation has been done to merge the two (by placing mouse brain cells on a specialized computer chip, which was placed into a mechanical shell), and the resulting combination moved on its own and even showed primitive thinking skills. Would such cybornetic combinations have free will as well?