The Old Firm is the collective name for the Glasgow football clubs Celtic and Rangers. The origin of the term is unclear but may derive from the commercial benefits of the two clubs' rivalry.

The two clubs are the most successful in Scotland, between them having won 97 Scottish League championships, 68 Scottish Cups and 41 Scottish League Cups. Interruptions to their ascendancy have occurred infrequently, most recently with the challenge of the New Firm of Aberdeen and Dundee United in the first half of the 1980s. Since the 1985–86 season one half of the Old Firm has won the Scottish League and since the 2005–06 season the Old Firm have finished in the top two places.

Rangers and Celtic have played each other 400 times: Rangers have won 159 matches, Celtic 144 matches and 96 have been draws. The two clubs normally compete four times a year in the SPL and have regularly met in Scottish cup competitions.

The clubs have large support bases around Glasgow but also have supporters clubs in most towns throughout Scotland and in many cities around the world. The presence of Rangers and Celtic has been estimated to be worth £120 million to the Scottish economy.

Old or OLD may refer to:

A business (also known as enterprise or firm) is an organization engaged in the trade of goods, services, or both to consumers. Businesses are predominant in capitalist economies, where most of them are privately owned and administered to earn profit to increase the wealth of their owners. Businesses may also be not-for-profit or state-owned. A business owned by multiple individuals may be referred to as a company, although that term also has a more precise meaning.

The etymology of "business" relates to the state of being busy either as an individual or society as a whole, doing commercially viable and profitable work. The term "business" has at least three usages, depending on the scope — the singular usage to mean a particular organization; the generalized usage to refer to a particular market sector, "the music business" and compound forms such as agribusiness; and the broadest meaning, which encompasses all activity by the community of suppliers of goods and services. However, the exact definition of business, like much else in the philosophy of business, is a matter of debate and complexity of meanings.