Seven Laws of Magic

The Laws of Magic are a set of rules of the White Council concerning the use of magic. They are intended to prevent the abuse of magic, and protect both practitioners and mortals from harmful magic. The White Council enforces the Laws not only on its own members, but on all human magical practitioners. The punishment for violating the Laws is often death.

First Law of Magic: "Thou Shalt Not Kill"
The First Law of Magic forbids the killing, specifically of humans, with magic.

Wizards of the White Council are forbidden to kill human beings through the use of their power. This is the Law that Harry Dresden broke in killing his mentor, Justin DuMorne (Justin Morningway, in the television series). Self-defense is very occasionally allowed as a mitigating factor, though the taint of killing another with magic often remains. This Law is also a primary reason Wardens wield swords. Several times throughout the series, Wardens have fought to kill with magic against other human wizards; it's possible Wardens are given somewhat of a free pass in regards to this Law in combat circumstances. The Law is very flexible, however, in regards to things that are not actually human. A wizard may kill, for example, a vampire, ghoul, or any being of the Nevernever without penalty.

If a person uses magic to kill another human the penalty is death. The trial, when one is held, lasts generally less than fifteen minutes and the execution is carried out immediately afterward by beheading.

Second Law of Magic: "Thou Shalt Not Transform Others"
The Second Law of Magic forbids the shapeshifting of other beings.

This demonstrates why, despite Harry's occasional threats, we will most likely never see him actually turn anyone into a frog. Even if done successfully (it is an extremely difficult spell), transformation of another's body against their will – changing a man into an animal, for example – creates an imbalance between body and mind that ultimately degrades the transformed subject's mind to an animal state as well. Transformation of oneself through magic is not necessarily as destructive, but still risky and potentially hazardous.

Third Law of Magic: "Thou Shalt Not Invade the Mind of Another"
The Third Law of Magic forbids the use of psychomancy.

Forcible magical violation of someone's mind by extracting knowledge against their will is inherently destructive – Harry describes it as not black, but "dark, dark, dark gray". Mind magic is so dangerous that the Council has not even dared trying to explore how to build better defenses, which gives an advantage to black wizards less bound by such scruples.

Fourth Law of Magic "Thou Shalt Not Enthrall Another"
The Fourth Law of Magic forbids the binding of any being against its will.

Enthrallment is the term for dominating another human's mind and personality through magic by binding their will to your own; it is not the same as compelling beings of the Nevernever through arrangements or exchanges. So long as the wizard in question does not actually control the being through magic, the law is not broken. A popular alternative is trapping the creature in a magic circle until it accepts the terms of a bargain, though some Wardens have ignored this distinction in their zeal. As with mind-probing, magically controlling the mind of another person is an inherently destructive and evil act – it is almost impossible to control safely and precisely, and taints the user of the power as well as the subject even if done for the best of intentions. This taint often sends the user into a self-destructive downward spiral, where every act of magical mind control further twists the user and makes more such acts likelier; if the cycle progresses far enough, the user becomes functionally sociopathic, and impossible to rehabilitate.

Fifth Law of Magic: "Thou Shalt Not Reach Beyond the Borders of Life"
The Fifth Law of Magic forbids the use of necromancy.

This Law covers the research and practice of necromancy, described as the summoning, binding, and exploitation of the unwilling dead. In the universe of the novels, nobody is presented as knowing for certain what kind of afterlife, if any, exists; ghosts, even the most apparently intelligent and self-aware, are stated to be only psychic echoes of people created by violent death, not the actual souls of those people themselves. As the Laws are intended to protect humans against the abuse of magic, a loophole in this law (exploited by Harry in Dead Beat) allows the use of necromancy on non-human dead, though the practice is still heavily frowned upon and viewed with a wary eye.

Sixth Law of Magic: "Thou Shalt Not Swim Against the Currents of Time"
The Sixth Law of Magic forbids time travel, with the purpose of avoiding the paradoxes due to any attempt to change the past through temporal manipulation. Even divination of the future is frowned upon in all but the vaguest, most general instances.

Seventh Law of Magic: "Thou Shalt Not Open the Outer Gates"
The Seventh Law of Magic forbids the summoning or contacting of Outsiders.

In Cold Days, the Outer Gates are revealed to be literal gates separating Creation from Outside. They are described as a large (possibly the largest) entrance to the universe. Set in a gigantic wall, between two towers each the size of the Chrysler building, they are powerfully warded, and constantly defended from Outsiders by the Gatekeeper and the immense army of the Winter Court. The Outer Gates function as a detector, and are enchanted in a way that allows them to infallibly reveal any Outsider that tries to sneak through. The Gatekeeper reveals to Dresden that his false eye is actually a shard of the Outer Gates, and that his title as Keeper of the Outer Gates is no mere metaphor or formality. If a Wizard breaks the Seventh Law and contacts or summons an Outsider, that Outsider gains a foothold in Creation without first having to pass through the Gates, making the Law-breaking Wizard responsible for endangering reality itself. There is only one penalty for breaking the Seventh Law of Magic, and that penalty is death.

Outsiders are beings from beyond the Gates, and are among the deadliest threats to humanity known – their sheer existence is antithetical to the universe. Jim Butcher has admitted that this is a Lovecraft-inspired idea, and the Necronomicon has been mentioned in Blood Rites and Backup as a book containing knowledge of Outsiders, and at least some of the beings living on the other side of the Gates are referred to as "Old Ones" by Harry. Even the mere knowledge of an Outsider's Name is dangerous for Creation due to the simple fact that the Name can be used to break the Seventh Law and allow an Outsider to bypass the Gates. The Oblivion War was started in order to erase any such knowledge from existence. According to Jim, the person who wrote the Necronomicon was killed by the Gatekeeper.

It appears that the Gatekeeper's primary responsibility is ensure no Outsider manages to enter Creation undetected, whereas the purpose of the entire Winter Court is to kill any and all Outsiders that try to approach the borders of reality. To accomplish this, Mab has an army garrisoned at the Gates so large that it eclipses the population of the entire Summer Court by several orders of magnitude. Outsiders have an immunity or at the very least considerable resistance to most mortal magic, thus most applications of magic versus Outsiders are often indirect. In Cold Days, Harry used Soulfire infused pyromancy to hurt an Outsider directly; thus it is possible that Soulfire is more effective in direct application versus Outsiders, unless it is simply Harry's status as a Starborn that allows him to harm Outsiders.

Titania revealed to Dresden that there is an Outsider on the loose that had managed to bypass the Outer Gates and infiltrate Creation without being detected. She outright refused to speak its true Name, instead referring to it as Nemesis. Nemesis is a viral contagion capable of "infecting" beings from Creation with a discordant influence that seems to both allow and motivate—if not outright compel—those infected to act in opposition to their innate purpose or nature. This infection allowed Maeve, a High Sidhe, to actively lie. Nemesis also demonstrated that it is capable of assuming direct control of an infected when Dresden encouraged Cait Sith to resist its influence. It is strongly hinted that The Circle is a group of entities that are infected by Nemesis.

In Cold Days, Mother Summer implies that the ultimate goal of the Outsiders is to break down the Outer Gates and bring about Empty Night.

General notes
Margaret LeFay strove for the Council to include more laws that would prevent injustices such as wizards bilking people out of their money, intimidating them, stealing, or destroying property. According to Luccio, the consequence of changing the Laws of Magic is that the Council would end up intervening in human affairs and ultimately into political affairs which would cause them to take the side of one country over another where there was perceived injustice. Seeing how the White Council had members in all countries, and that the wizards had no better idea of who was right or who was wrong then any other human, this would have been a disaster, and it would force members to turn on their own. The Council would descend into civil war and likely break apart. There would then be no protection for humanity against magic or the supernatural world.

Another consequence would be that if the council involved itself in mortal affairs it would seek more political power, more control, and there is no better tool for gaining more power than black magic. So the council limits itself: Any wizard is free to act as he chooses, as long as he doesn't break the Laws of Magic. Sans black magic, there is a limit to how much damage an individual can perpetrate against a mortal society. Neither the Laws nor the White Council are about justice, they are about restraining power.

In Changes, Ebenezar McCoy told Harry that what's going on in Edinburgh could be the end of organized Wizardry and the end of the Laws of Magic.