The Inquisition was a office of the Catholic Church charged with suppressing heresy. There have been four different Inquisitions; their actions and interactions with the local governments are subjects of considerable historical enquiry.
The infamous Spanish Inquisition was not an ecclesiastical operation at all. It was established in 1481 by Ferdinand and Isabella to investigate and punish the Jews and Moors who had publically converted to Christianity but had privately continued to practice their prior religion and were thus, by definition, heretics. Jews or Muslims who did not become Christians were never subjected to the powers of the Inquisition.
Less known is the Portugese Inquisition, which rivaled the Spanish in its infamy.
- Edward M. Peters, Inquisition. (University of California Press, 1989). ISBN: 0520066308
- ---A brief, balanced inquiry, with an especially good section on the 'Myth of the Inquisition'. This is particularly valuable because much of the history available in English of the Inquisition was written in the 19th century by Protestants interested in documenting the dangers of Catholicism or Catholic apologists demonstrating that the Inquisition had been an entirely reasonable judicial body without flaws.
- Henry Kamen, The Spanish Inquisition: A Historical Revision. (Yale University Press, 1999). ISBN: 0300078803
- ---This revised edition of his 1965 original contributes to the understanding of the Spanish Inquisition in its local context.