What was the title of Galileo's last major work?

Galileo's last major work was Two New Sciences. Published in 1638, the book gathered decades of his research into motion, mechanics, and the strength of materials.

Its full title was Discourses and Mathematical Demonstrations Relating to Two New Sciences. Galileo presented the material as a dialogue among Salviati, Sagredo, and Simplicio, a format he had also used in his earlier Dialogue Concerning the Two Chief World Systems. The book examined how objects move and why structures fail or support loads.

Two New Sciences was published in Leiden by the Elzevir press because the Roman Inquisition had restricted publication of Galileo's works. Its studies of falling bodies, projectile motion, and material strength helped establish mathematical physics. A common mix-up is choosing Dialogue Concerning the Two Chief World Systems, which was Galileo's famous earlier work on the Copernican controversy, not his final major book.