In 1564 Galileo was born in Pisa, where his schooling began. In 1574 he began to study in Florence with the Vallombrosan monks, but was taken away by his father before he had completed his course of study.

In 1580 Galileo enrolled in the Faculty of Medicine and Philosophy at the Studio of Pisa (the University) but, strongly attracted to the study of geometry and disappointed with the academic milieu, he failed to complete the course. He began a deeper study of Archimedes' work which offered him a methodological basis opposed to the dominant Aristotelian philosophy. He wrote La bilancetta [The Little Balance] and the Theoremata circa centrum gravitatis solidorum [Theorems concerning the Centre of Gravity of Solids], which however were not published.

In 1589 Galileo was appointed to the Chair of Mathematics at the University of Pisa, where he began to study phenomena related to the motion of bodies. But, poorly paid and at odds with his colleagues, he opted for transfer to the University of Padua.

At Padua from 1592 onwards, Galileo engaged in public and private teaching, giving lessons in mechanics, the art of war and cosmology. He continued his research on the motion of falling bodies and began seriously to doubt the truth of the Aristotelian-Ptolemaic system, considering it less probable than the Copernican. He became involved in his first scientific controversies regarding the nova of 1604 and his invention of the geometric and military compass.

At Padua Galileo built his first telescope and observed the heavenly bodies. In 1610 he published the Sidereus nuncius [The Starry Messenger], announcing his discoveries, which contradicted Ptolemy in favour of Copernicus. In 1610 he was summoned to Florence as Chief Mathematician and Philosopher to the Grand Duke of Tuscany.

In Florence from 1610, Galileo continued his cosmological studies and in 1611 went to Rome, where his discoveries were at first welcomed favourably.

In conflict with the Florentine Aristotelians, Galileo printed a number of texts on the behaviour of floating bodies. In 1613, with the Istoria e dimostrazioni intorno alle macchie solari e loro accidenti [History and Demonstrations concerning Sunspots and their Phenomena], he opposed the ideas of the Jesuit, Christoph Scheiner, and confronted problems of scientific method, for the first time explicitly advocating the truth of the Copernican system.

Drawn into argument by certain anti-Copernican, Florentine Dominicans, Galileo took a stand on the relationship between scientific theories and the holy texts, advocating the independence of science in relation to theological interpretation of Scripture. He wrote, but did not publish, the Lettera a Benedetto Castelli [Letter to Benedetto Castelli] and the Lettera a Cristina di Lorena [Letter to Christine of Lorraine].

Galileo was denounced to the Inquisition and in 1616, following a trial, he was warned not to argue the truth of Copernican thought, declared to be false. Copernicus’ De revolutionibus was suspended pending correction.

Galileo became involved in a controversy on the nature of comets. In 1619 he published anonymously the Discorso sulle comete [Discourse on Comets], in which he expressed opposition to the Tychonic system, on which the Jesuits had fallen back after Ptolemy's system had been proved unsustainable.

The debate over comets continued, culminating in 1623 with the publication of Il Saggiatore [The Assayer] in which Galileo made a forceful attack on the Jesuits in regard to scientific method. The response he received was an attack on the theological level.

In 1623 Cardinal Maffeo Barberini was elected pope under the name of Urban VIII. Galileo counted on his support to rehabilitate Copernicus and to demonstrate the truth of his own world system. But the Pope was not as open in his thinking as he had earlier appeared.

In 1632 the Dialogo sopra i due massimi sistemi del mondo [Dialogue concerning the Two Chief World Systems] was published, in which Galileo, being unable to sustain openly the truth of the Copernican system, presented it instead as the most plausible hypothesis, pointing out the indefensible nature of the Aristotelian-Ptolemaic position.

The Dialogue concerning the Two Chief World Systems was not received favourably in Rome. The Pope, in the midst of a difficult political crisis, was infuriated to find that his personal opinions had been treated disrespectfully by Galileo. A commission of theologians examined the work and found grounds in it for numerous charges. The issue was handed over to the Inquisition, which set in motion preparations for a trial.

Galileo arrived in Rome, where he was confined and tried in 1633. The trial took an unexpected turn and Galileo was forced in the end to yield. But he never confessed to having maintained the truth of the Copernican system. Nonetheless, he was found guilty and the Dialogue prohibited.

Galileo abjured his scientific convictions, declaring that never again would he study the motion of the Earth, now deemed heresy. The publication of his writings was forbidden, but outside Italy this veto was not observed.

Galileo was confined to his villa at Arcetri. No longer able to engage in cosmological issues, he resumed his studies on the motion of falling bodies and in 1638 published in Leyden the Discorsi e dimostrazioni matematiche intorno a due nuove scienze [Discourses and Mathematical Demonstrations concerning Two New Sciences]. Although now suffering from an incurable eye disease, he continued his studies to the end. He died, isolated and blind, in 1642.

The effects of the judgement against Galileo were felt for many years after his death, profoundly influencing the direction study in general took within the sphere of influence of the Church of Rome.