Ruth d'Ans is best known as the disciple and secretary of Antoine Arnauld but survived his master by more than three decades to become a key member of the Jansenist Internationale in the difficult years after publication of the papal bull Unigenitus in 1713. He was a networker, a traveller, an intriguer and a tactician rather than a theologian, and Michel Van Meerbeeck has brought him to the centre stage again in this exhaustive (and somewhat over-minute) study of his career that makes systematic use of the rich archival holdings of Belgium. Ruth d'Ans was from the principality of Liège, a graduate of the University of Louvain, and his Jansenism was primarily the product of his social and educational associations and the relatively tolerant 1670s following the so-called ‘Peace of the Church’ in 1669. He made his first visit to Port-Royal des Champs in 1676 and served resourcefully as secretary to Arnauld (who lived in the United Provinces and then in Brussels after his exile from France in 1679) until the latter's death in 1694. This attachment ensured that Ruth d'Ans's career thereafter was never going to be sedate. He managed to secure a canonry of Saint-Gudule but could not escape the censorious notice either of the archbishop of Malines or of the secular authorities both before and after the Bourbon succession to the Spanish Netherlands in 1700. Life became slightly more comfortable after the Habsburgs took control of the region after 1706 and Ruth d'Ans found favour with Prince Eugène of Savoy. He even enjoyed some protection from the emperor Charles vi until Unigenitus was published in the Austrian Netherlands in 1723. Ruth d'Ans was a key member of the Jansenist Paris–Brussels–Utrecht axis in his later years and scholars interested in the origins of the Old Catholic Church of Utrecht will find in Van Meerbeeck's biography abundant information about the complicated Catholic currents of the years preceding its foundation.