Francesco di Giorgio Martini is one of the few fifteenth century Sienese artists who became known outside his native city. Working at the courts of Urbino, Naples and Milan, he was a typical Renaissance "uomo universale" but his major achievements were in military and civil architecture, complemented by the composition of a theoretical treatise. The collection of essays does not offer a comprehensive study of the artist's architectural oeuvre, but rather emphasizes the partial nature of the scholarly endeavor so far undertaken. The essays discuss Francesco's theory, his drawings from the antique, the individual characteristics of his practice, and the reception of his work. They share a common idea: invention, which emerges as a valid theoretical framework, possibly the only one capable of encompassing Francesco di Giorgio's versatile accomplishments.