Football in Scotland has been dominated by two clubs, Celtic and Rangers, both based in Glasgow and collectively known as the Old Firm due to the mutual economic benefits of the public interest in their longstanding rivalry, since the introduction of a national league system in 1890. While many of the league contests have been closely fought between the pair and have occasionally involved other clubs, periods of one-team dominance have occurred, most significantly three periods of nine championship wins in succession since the 1970s which has led to the term "Nine in a row" becoming a commonly-used phrase, and a topic which has drawn much attention.

The Celtic Football Club, commonly known as Celtic, is a professional football club in Glasgow, Scotland. The team competes in the Scottish Premiership, the top division of Scottish football. The club was founded in 1887 with the purpose of alleviating poverty in the Irish–Scots population in the city's East End area. They played their first match in May 1888, a friendly match against Rangers which Celtic won 5–2. Celtic established themselves within Scottish football, winning six successive league titles during the first decade of the 20th century. The club enjoyed their greatest successes during the 1960s and 70s under Jock Stein, when they won nine consecutive league titles and the 1967 European Cup. Celtic have played in green and white throughout their history, adopting in 1903 the hoops that have been used ever since.