Henri Matisse described the Chapel of the Rosary, the chief labour of his final years, as the 'gathering together' of his lifetime's work. Although widely known as 'Matisse's Chapel', the building's remarkable modern design and decoration emerged from a surprising friendship and artistic engagement with a group of Dominican sisters and brothers keen to see the Church embrace modern art and modern artists. With the advantage of hitherto unexplored archive and printed materials, this study highlights that mutual encounter and explores how their shared artistic adventure became for Matisse an opportunity to express his 'religious' vision of art and to rediscover his natal Catholic Faith in its post-war avant-garde form.