Book excerpt: Travelling through the history of art from the 15th to the 20th century, this book is a survey of works of art by Old and Modern Masters including Van Eyck, Leonardo, Michelangelo, Rubens, David, Manet, Cézanne, Matisse and Mondrian that have remained deliberately or unintentionally unfinished, and that are usually marginalized in traditional art history. They remain incomplete for various reasons: illness or death of the artist; political turmoil forcing him to flee; disagreements with the commissioner or dissatisfaction with the artistic result. However, from the 16th century onwards, artists started to use the non finito as a tool of expression. Unfinished pictures therefore gained a certain reputation in the romantic era, when they were thought to offer the spectator a glimpse of artistic genius. In the 20th century, these paintings were discovered by cubists, expressionists and abstract painters who were fascinated by their rough and incoherent appearance, often unaware of their history.