Foucault begins by comparing a public execution from 1757 to an account of prison rules from 1837. The shifts between the two reveal how new codes of law and order developed. One important feature is the disappearance of torture; the body of the criminal disappeared from view. Punishment as spectacle disappeared; the exhibition of prisoners, the pillory and the public execution ended. Now, the certainty of punishment, and not its horror, deters one from committing a crime. Conviction marks the prisoner; publicity shifts towards the trial and the sentence.

A theoretical realignment occurs. Sentences are now intended to correct and improve. A sense of shame about punishment develops along with this. Punishment no longer touched the body. If it did, it was only to get at something beyond the body: the soul. New figures took over from the executioner, such as doctors, psychiatrists, chaplains and warders. Executions were made painless by drugs. The elimination of pain and the end of spectacle were linked. Machines like the guillotine, which kills almost without touching the body, were intended to be impersonal and painless. Between 1830 and 1848, public executions ended. This was an irregular, delayed process, however. A trace of torture remained because it is difficult to imagine what a non-corporal punishment would be.

The penalty now addressed the soul. Although the definition of crimes changed, some elements remained the same. Judgment was now passed on the motives, passions and instincts of the criminal, not only punishing but also supervising and directing the individual. Offenses became objects of scientific knowledge. The development of a new penal system in Europe led to the soul of the criminal as well as the crime being judged.

The power to punish becomes fragmented. Psychiatrists now decide on a criminal's medico-legal treatment. The adoption of these non-legal elements meant that the judge is not the only one who acts or judges.

This book is a genealogy of the modern soul and the power to judge. It follows four general rules: one) to regard punishment as a complex social function; two) to regard punishment as a political tactic; three) to see whether the history of penal law and of the human sciences are linked; four) to try to find in changes in penal techniques a political technology of the body and a general history of changing power relations. We need to situate punishment within systems of production and the political economy of the body. Historians have yet to consider the body as a subject of political power or power relations. The body is subjected to a body of knowledge; this is the political technology of the body. A "micro-physics" of power operates; power is a strategy, and we need to decipher it in a system of relations that can be called political anatomy. Power is not a property but a strategy evident in the relations between people. Power relations operate and exist through people. They go right down into society. We need to realize that power and knowledge are related. We should think of the body politic as a series of routes and weapons by which power operates.

A history of the micro-physics of power is an element in the genealogy of the modern soul. Upon the idea of the "soul", concepts of the psyche, personality and consciousness are created, as well as scientific techniques and claims. This is not a substitution of the soul for the real man; now, the soul is the prison of the body. Foucault ends by relating his commitment to modern prisoners, and to writing a history of the present.