Simony is the sin of buying or selling holy offices for money. It is named after Simon Magus, who attempted to buy his way into the early church, as reported in the Book of Acts (Acts 8:18-20). Simony is not often heard of in the modern day, but in previous centuries when bishops and cardinals held great temporal power it was often widespread. In his Inferno, Dante condemns several Popes of the time for this sin, although Simon Magus himself is punished for the worse crime of sorcery.
The Medieval practice of selling indulgences can also be considered a form of simony.