Book excerpt: Joachim of Fiore (c.1135-1202) remains one of the most fascinating and enigmatic figures of medieval Christianity. In his own time, he was an influential advisor to the mighty and powerful, widely respected for his prophetic exegesis and decoding of the apocalypse. In modern times, many thinkers, from Thomas Müntzer to Friedrich Engels, have hailed him as a prophet of progress and revolution. Even present-day theologians, philosophers and novelists were inspired by Joachim’s vision of a Third Age of the Holy Spirit. However, at no time was Joachim an uncontroversial figure. Soon after his death, the church authorities became suspicious about the explosive potential of his theology, while more recently historians held him accountable for the fateful progressivism of Western Civilization. Contributors are: Frances Andrews, Valeria De Fraja, Alfredo Gatto, Peter Gemeinhardt, Sven Grosse, Massimo Iiritano, Bernard McGinn, Matthias Riedl, and Brett Edward Whalen.