Common sense tells us that we exist outside of the material world—we are connected to our bodies and our brains, but we are not ourselves material beings, and so we can act in ways that are exempt from physical law. For every decision we make—from leaning over for a first kiss, to saying “no” when asked if we want fries with that—our actions are not determined and not random, but something else, something we describe as chosen.
This is what many call free will, and most scientists and philosophers agree that it is an illusion. Our actions are in fact literally predestined, determined by the laws of physics, the state of the universe, long before we were born, and, perhaps, by random events at the quantum level. We chose none of this, and so free will does not exist.
I agree with the consensus, but it's not the big news that many of my colleagues seem to think it is. For one thing, it isn't news at all. Determinism has been part of Philosophy 101 for quite a while now, and arguments against free will were around centuries before we knew anything about genes or neurons. It's long been a concern in theology; Moses Maimonides, in the 1100s, phrased the problem in terms of divine omniscience: If God already knows what you will do, how could you be free to choose?
More important, it's not clear what difference it makes. Many scholars do draw profound implications from the rejection of free will. Some neuroscientists claim that it entails giving up on the notion of moral responsibility. There is no actual distinction, they argue, between someone who is violent because of a large tumor in his brain and a neurologically normal premeditated killer—both are influenced by forces beyond their control, after all—and we should revise the criminal system accordingly. Other researchers connect the denial of free will with the view that conscious deliberation is impotent. We are mindless robots, influenced by unconscious motivations from within and subtle environmental cues from without; these entirely determine what we think and do. To claim that people consciously mull over decisions and think about arguments is to be in the grips of a prescientific conception of human nature.
I think those claims are mistaken. In any case, none of them follow from determinism. Most of all, the deterministic nature of the universe is fully compatible with the existence of conscious deliberation and rational thought.