Journal article: One of the world’s most legendary derbies, based on a politico-religious rivalry, is the match between Celtic and Rangers in Glasgow. However, the first matches at the end of the 19 th century were above all popular and commercial successes, hence the name “The Old Firm”, symbolising the shared financial interests of the two clubs in the Scottish capital. It wasn’t until some twenty years later, in the 1910s, that the antagonism really came to the fore : Green vs. Blue, Catholic vs. Protestant, Republican vs. Unionist. Even though “The Old Firm” has lost some of its European lustre, both in sporting and economic terms, it remains a popular success that generates substantial income on match days. The rivalry, still essential to this success, has also changed in nature : as society has become less religious, “The Old Firm” has become its own generator of “sectarianism”.