The Reason of State (Italian: Della Ragion di Stato) is a work of political philosophy by Italian Jesuit Giovanni Botero published in 1589. The book first popularized the term "reason of state", which refers to the right of rulers to act in ways that go against the dictates of both natural and positive law, with the overriding aim of acquiring, preserving, and augmenting the dominion of the state to be used for the public welfare. This way of thinking about government morality emerged at the end of the fifteenth century and remained prevalent until the eighteenth century. Botero supports the political role of the Catholic Church and criticizes the immoral methods of statecraft associated with Niccolò Machiavelli.

Della Ragion di Stato was first published in Venice in 1589 and quickly became a political bestseller, going through 15 Italian editions and translations into Spanish, Latin, and French in the late sixteenth and the seventeenth centuries, as well as the German edition Johannis Boteri Grundlicher Bericht Anordnung guter Polizeien und Regiments of 1596.

Despite its success on the continent, the book was never published in England. There is a contemporary English translation by Richard Etherington found in a manuscript in the British Library. This translation is described as an 'Abstract' and is followed by Etherington's own response in an 'Adjunct'. There is a complete translation by William Lawrence from 1659, also found only in manuscript. Botero's treatise has been translated into English by P. J. and D. P. Waley with an introduction by D. P. Waley (London, 1956), and, more recently, by Robert Bireley (Cambridge, 2017).

In the dedication of the 1589 edition of The Reason of State, Botero states his determined opposition to Machiavellianism, to which he traces the corruption of 16th century political discourse.

However, Botero does adopt some aspects of Machiavelli's thought. For instance, in 1590 Botero added a chapter that advocates all European states join the Republic of Venice in a campaign to oust the Ottoman Empire from Europe. This appeal mirrors Machiavelli's own call to drive all foreigners out of Italy at the end of The Prince. Botero also expands upon Machiavelli's idea that men, not money, are more important for preserving a political regime. Where for Machiavelli men are crucial as soldiers, Botero proclaims that both a regime's population and its martial abilities are the most crucial resources at a ruler's disposal.

Botero states his intention to bring to light the surreptitious discussions of "reasons of state" common in European courts, which were frequently influenced by Niccolò Machiavelli's political thought. To Machiavelli's instrumental, immoral principles, Botero presents an opposing Christian reason of state, in which statesmen are responsible before God and their conscience. He rejects any reasons of state which consistently transgress God's laws. In stark contrast to Machiavelli, Botero embraces Christianity and the Roman Catholic Church:

The prince must prostrate himself in all humility before the Divine Majesty and acknowledge that from Him proceed the power of a ruler and the obedience of his subjects ... A Christian prince [should not] close the door of his secret council-chamber against Christ and the Gospels and set up a reason of State contrary to God's law, as though it were a rival altar ... So great is the power of religion in government that the state can have no secure foundation without it ... Religion is the mother ... of all the virtues.

— Giovanni Botero, The Reason of State, translated by P.J. Waley and D.P. Waley, New Haven, Yale University Press 1956, p. 63.