Publications
The Verri brothers and Beccaria started an important cultural reformist movement centered around their journal Il Caffe, which ran from the summer of 1764 for about two years, and was inspired by the Spectator and other such journals. Il Caffe represented an entirely new cultural moment in northern Italy. With their Enlightenment rhetoric and their balance between topics of socio-political and literary interest, the anonymous contributors held the interest of the educated classes in Italy, introducing recent thought such as that of Voltaire and Diderot.

In 1764 Beccaria published a brief but justly celebrated treatise Dei Delitti e delle Pene ("On Crimes and Punishments"), which marked the high point of the Milan Enlightenment. In it, Beccaria put forth the first arguments ever made against the death penalty. His treatise was also the first full work of penology, advocating reform of the criminal law system. The book was the first full-scale work to tackle criminal reform and to suggest that criminal justice should conform to rational principles. It is a less theoretical work than the writings of Grotius, Pufendorf and other comparable thinkers, and as much a work of advocacy as of theory. In this, Beccaria reflected the convictions of the Il Caffe group, who sought to cause reform through Enlightenment discourse. The book's serious message is put across in a clear and animated style, based in particular upon a deep sense of humanity and of urgency at unjust suffering. This humane sentiment is what makes Beccaria appeal for rationality in the laws.

Within eighteen months, the book passed through six editions. It was translated into French by André Morellet in 1766, and published with an anonymous commentary by Voltaire. An English translation appeared in 1767 and it was translated into several other languages.

The book was read by all the great luminaries of the day, including, in the United States, by John Adams and Thomas Jefferson.

Policies and later life
The principles to which Beccaria appealed were Reason, a contractarian understanding of the state, and, above all, the principle of utility, or of the greatest happiness for the greatest number. Beccaria had elaborated this original principle in conjunction with Pietro Verri, and greatly influenced Jeremy Bentham to develop it into the full-scale doctrine of utilitarianism.

Apart from condemning the death penalty (on two grounds: first, because the state does not possess the right to take lives; and secondly, because capital punishment is neither a useful nor a necessary form of punishment), Beccaria developed in his treatise a number of innovative and influential principles: punishment had a preventive, not a retributive, function; punishment should be proportionate to the crime committed; the certainty of punishment, not its severity, would achieve the preventive effect; procedures of criminal convictions should be public; and finally, in order to be effective, punishment should be prompt.

With the Verri brothers, Beccaria traveled to Paris, where he was given a very warm reception by the philosophes. He retreated in horror, however, returning to his young wife Teresa and never venturing abroad again. The break with the Verri brothers proved lasting; they were never able to understand why Beccaria had left his position at the peak of success.

Many reforms in the penal codes of the principal European nations can be traced back to Beccaria's treatise, although few contemporaries were convinced by Beccaria's argument against the death penalty. When the Duchy of Tuscany abolished the death penalty, as the first nation in the world to do so, it followed Beccaria's argument about the lack of utility of capital punishment, not about the state's lacking right to execute citizens.

In November 1768 Beccaria was appointed to the chair of law and economy, founded expressly for him at the Palatine college of Milan. His lectures on political economy, which are based on strict utilitarian principles, are in marked accordance with the theories of the English school of economists. They are published in the collection of Italian writers on political economy (Scrittori Classici Italiani di Economia politica, vols. xi. and xii.). Beccaria never succeeded in producing a work to match Dei Delitti e Delle Pene, although he made various never completed attempts in the course of his life. A short treatise on literary style was all he saw to press.

In 1771 Beccaria was made a member of the supreme economic council; and in 1791 he was appointed to the board for the reform of the judicial code, where he made a valuable contribution. He died in Milan.