Mill starts off by limiting the scope of his essay to Civil, or Social Liberty. He writes that this essay will look at what kind of power society can legitimately exert over the individual. Mill predicts that this question will become increasingly important because some humans have entered a more civilized stage of development, which presents "new conditions" under which issues of individual liberty must be addressed.

Mill then turns to an overview of the development of the concept of liberty. In ancient Greece, Rome and England, liberty implied "protection against the tyranny of political rulers," and rulers and subjects were often thought to have a necessarily antagonistic relationship. The leader did not govern by the will of his people, and while his power was seen as necessary, it was also considered dangerous. Patriots tried to limit the leader's power in two ways: 1) They gained immunities called "political liberties or rights." The leader was thought to have a duty to respect these immunities, and there was a right of rebellion if these rights and liberties were infringed. 2) Constitutional checks developed, under which the community or their representatives gained some power of consent over important acts of governance.

Mill writes that eventually men progressed to a point where they wanted their leaders to be their servants, and to reflect their interests and will. It was thought that it was not necessary to limit this new kind of ruler's power, because he was accountable to the people, and there was no fear of the people tyrannizing itself. However, when an actual democratic republic developed (The United States), it was realized that the people don't rule themselves. Rather, the people with power exercise it over those without power. In particular, a majority may consciously try to oppress a minority. Mill writes that this concept of a tyranny of the majority has come to be accepted by major thinkers. Mill, however, argues that society can also tyrannize without using political means. Rather, the power of public opinion can be more stifling to individuality and dissent than any law could be. Thus, he writes that there must also be protection for people against the prevailing public opinions, and the tendency of society to impose its values on others.

The question, then, as Mill sees it, is where and how to limit public opinion's sway over individual independence. There has been very little consensus among nations about the answer to this question, and people tend to be very complacent about their own customs in dealing with dissent. People tend to believe that having strong feelings on a subject makes having reasons for that belief unnecessary, failing to realize that without reasons their beliefs are mere preferences, often reflecting self-interest. Furthermore, on the occasions when individuals do question the imposition of public opinion on social standards, they are usually questioning what things society should like or dislike, not the more general question of whether society's preferences should be imposed on others. Mill also notes that in England there is no recognized principle by which to judge legislative interference in private conduct.

After laying out the major issues, Mill then turns to what he calls "the object of his essay." He writes that he will argue that the only time individuals or society as a whole can interfere with individual liberty is for self-protection. Mill states that the argument that a certain law or public opinion might be for an individual's own good or welfare does not suffice to justify that law or public opinion as a coercive force; coercion by the many toward the individual is only acceptable when an individual poses a threat to others. It is fine to argue with a person about his actions, but not to compel him. Mill writes, "Over himself, over his own body and mind, the individual is sovereign."

Mill notes that the right of liberty does not apply to children, or to "backward" societies. It is only when people are capable of learning from discussion that liberty holds; otherwise the people must be taken care of. Mill also notes that he is not justifying the claim of liberty as an abstract right. Rather, he is grounding it in utility, on the permanent interests of mankind.

Mill writes that if a person causes harm to others actively or inactively, it is appropriate for society to condemn him legally or through general disapprobation. Individuals can even be compelled to do good for other people, such as to save someone's life, because to do otherwise would be to cause evil to another person. In contrast, society only has an indirect interest in what a person does to himself or to other freely consenting people.

Mill divides the appropriate sphere of human liberty falls into three categories, claiming that any free society must respect all three. First, there is the domain of the conscience, and liberty of individual thought and opinion. Second, there is planning one's own life, and the liberty of tastes and pursuits. Third, there is the liberty to unite with other consenting individuals for any purpose that does not harm others. These liberties reflect the idea that true freedom means pursuing one's own good in one's own way, as long as it does not prevent others from doing the same. These ideas directly contradict society's increasing tendency to demand conformity, and unless moral conviction turns against this tendency, the demand for conformity will only increase.

Mill's introduction is one of the most important parts of his essay, as it contains the basic structure of his argument, as well as some of his major presuppositions. Mill describes civilization as a struggle between society and the individual about which should have control over the individual's actions. Mill sees the world as tipping toward a balance in which society, through laws and public opinion, has far more power over the actions and thoughts of an individual than an individual has over himself. Mill rejects this status, arguing that society should have control over only those actions that directly affect it, or those actions that harm some of its members. Mill argues that an individual harming himself or acting against his own good provides insufficient reason for others to interfere. His essay will be a description of why this is the case.

It is important to note that in rejecting social interference with individual thought and activity, Mill is not just writing about laws, but also about "moral reprobation." An individual or group cannot rightly punish a person's behavior by, for example, treating him as an enemy, if his actions only affect himself. In rejecting the legitimacy of coercive opinion, Mill drastically broadens the scope of his claims. It is worth paying attention in later chapters to why Mill is so critical of public disapproval of behavior, and to the avenues that Mill does leave open for people to express disapproval of actions they dislike.

The idea of progress is integral to Mill's essay, and this chapter reflects a few of his ideas on the subject. Mill believes that individuals and society as a whole can improve themselves. Fitting with this idea, he considers different societies to exist on a clear hierarchy of value: barbaric societies are childlike, without the necessary tools of self-government. They must be governed like children, so that they can eventually become capable of exercising their liberty. Yet while Mill considers progress and civilization to be definite goods, he also expresses concern that with progress comes conformity. In later chapters he will try to show that such conformity could undermine further individual and social improvement.

In this introduction, Mill explicitly calls his justification of liberty utilitarian. In doing so, he says outright that his defense of liberty will not be based on natural rights, such as those proposed by Locke, or on metaphysical claims, such as those proposed by Kant. Rather, Mill bases his argument on what is best for mankind, and in doing so suggests that his arguments will show the individual and social benefits of human liberty. In later chapters, it is worthwhile to examine when and how Mill makes broad utilitarian arguments for liberty, and to similarly look for instances when Mill resorts to non-utilitarian arguments.