I have just published an article on 11th-century simony (the illicit purchase of ecclesiastical office) in the Journal of Ecclesiastical History. The article argues that the ‘simony crisis’ was imported into Italy along with the German popes in the mid eleventh century, and amplified across the Latin west from there. You can read it here (£).
The article explores the issue through an important work known as the ‘Letter of Guido’, which it suggests might date to the 1060s rather than the 1030s. To accompany the article, I’ve drafted an English translation of this text, and I’ve posted this translation here (opens pdf).