Peter Paul Rubens (1577-1640) is the most important painter of sketches in the history of European art. His Italian and Flemish predecessors had for the most part prepared their paintings by using drawings. Rubens transformed this process by systematically making sketches in colour, with oil paint, and nearly always on panel supports. Rubens's oil sketches were essentially a new form of painting. They brought together the design and colour stages of preliminary work. Because their purpose was to advance another work of art, oil sketches demanded less effort and time than the final products, and this translated into a less polished finish and smaller size. Rubens's sketches invite us to indulge in his art. They are powerful, vivid renditions of a variety of themes, from ancient history and mythology to religion, still life and portraits. They combine seriousness of purpose and a zest for life, transmitted through a masterly lightness of touch. Their small size and appearance of incompleteness draw us in and entice us to look closely. Their sheer quality is a great source of pleasure and learning. This catalogue presents detailed studies and superb illustrations of eighty-two of Rubens's most eloquent oil sketches, and two essays explaining the historical context from which they emerged, their salient features and how they were viewed by contemporaries. Friso Lammertse is Curator of Old Master Paintings and Sculpture at Museum Boijmans Van Beuningen in Rotterdam. Alejandro Vergara Sharp is Senior Curator of Flemish and Northern European Paintings at the Museo Nacional del Prado in Madrid.