What is Jansenism, and what is the heresy behind it?
Jansenism is the incorporation of the extreme predestination doctrines of Calvinism into Catholicism. It started in France and the Low Countries in the 17th Century. Basically it taught a limited atonement whereby Christ died only for the Elect, not for everyone, and those who were to be saved had been chosen by God at the beginning of time.
The theories of Jansenism caused great division, particularly in France, where Calvinism had been strong. jansenisy doctrines were condemned Jansenism was condemned as heretical in several papal bulls, notably by Pope Innocent X, Alexander VII and Clement XI.