On 26 January 1622, in Paris, Rubens entered into a contractual agreement to execute two series of monumental paintings, ‘in his own hand’, intended to decorate the two parallel galleries of the Parisian palace - the so-called Luxembourg Palace - of Maria de Medici, widow of Henry IV and mother of Louis XIII. Completed in 1625, the 24 paintings of the West Gallery exalting the life of the queen mother form a universally admired ensemble, on display at the Louvre for two centuries. However, the second part of this grand project, envisioned for the East Gallery of the palace of the queen mother, was abandoned in 1630. The suspension of the project, definitively terminated after the queen mother’s exile in July 1631, has deprived us of a work absolutely unique both in its magnitude and in the artistic means deployed by the artist for the glorification of the royal couple. The Galerie Henri IV, the aim of which was the celebration of the military victories of the king and the exaltation of his triumphs ‘in the manner of the triumphs of the Romans’ (according to the terms of the contract) remains a puzzle whose missing pieces are more numerous than those that have been preserved. The object and aim of the present volume, notably through the study of about fifteen preparatory sketches and paintings, more or less completed, that have come down to us, are to better understand the place, the immediate meaning and the political significance of the Galerie Henri IV, which remains, to our great frustration (no less than that of Rubens), an extraordinary encomiastic baroque ‘machine’, and undoubtedly the unfinished masterpiece of the artist.