This is in part a question about how the AI works, and another part a suggestion on a possible AI improvement. Question I can see that each leader has a favorite religion, but I am wondering how this mechanic works in practice : 1) Do they have to discover the religion to switch to it? For instance if I discovered Islam and have the holy city, will Saladin convert to Islam even though he used something like buddhism for the whole game? 2) Does it make a difference if he founded buddhism or someone just spread it to him? 3) Does switching religion to the favorite one depend on the number of cities where it is present? Again in the saladin example, do I have to significantly spread it to him so he can switch or will a couple of cities suffice? 4) Does it take into account the possible income loss (if Saladin has the buddhism holy city) from switching to the favorite religion? 5) Does it take into account that switching religion can alienate it towards other AIs and possibly even start wars by becoming the worst enemy of someone? (the diplomatic situation) 6) Will it switch by itself eventually or do I have to ask for it through the diplomacy screen? 7) Do I get extra diplomatic points if I have an AI's favorite religion? (Again if Saladin is a Buddhist and I have Islam as state religion) I want to use the favorite religion factor to my advantage in game and thus it would be great to know as much as possible about how it works. Suggestion for better AI FavoriteReligion is obviously a simple roleplay addition to give the different AIs some personality... It is an arbitrary choice at best and in order to provide a better challenge it should mimic an experienced human player that chooses his religion (or lack of) rationally. I am not familiar with the AI programming, so my apology if it is already doing this... But if it isn't I think the FavoriteReligion variable should be disabled/ignored at higher difficulty levels (I suggest monarch+) entirely. Or even better the AI should switch its own "FavoriteReligion" to the religion that would best serve its interests taking into account factors like diplomacy, its desired allies, and the military power situation.