The rivalry between Glasgow's "Old Firm" sides is perhaps the most famous derby in the entire world of football. It's the game's flagship conflict, proof of the power of the sport to inspire profound levels of tribal loyalty and a near-Pavlovian revulsion at anything to do with a rival.In Rivals: Rangers & Celtic we examine the situation and try to get a handle on the political, religious and national identity clashes that have shaped the rivalry, speak to fanzine editors on both sides of the divide and travel with the Bhoys' away support to a match at Tannadice.