There is a lot of talk about heresy these days. The frequency and volume of accusations suggest that some Christians have lost a sense of the gravity of the word. On the other hand, many believers have little to no familiarity with orthodox doctrine or the historic distortions of it. What's needed is a strong dose of humility and restraint, and also a clear and informed definition of orthodoxy and heresy. Know the Heretics provides an accessible 'travel guide' to the most significant heresies throughout Christian history.