Idrottsföreningen Elfsborg, more commonly known as IF Elfsborg or simply Elfsborg (Swedish pronunciation: [ˈɛ̌lfsbɔrj]), is a professional football club based in Borås, Sweden, and is affiliated to the Västergötlands Fotbollförbund. They play in the Allsvenskan and have spent most of their history in the top tier of Swedish football. Their homeground is Borås Arena, where they have played since 17 April 2005.

The club was founded in 1904 by a group of 19 youngsters which all were 14–15 years old. Borås Fotbollslag was formed in Ordenshuset at Landala (today Knalleland) on 26 June 1904. The main protagonist in the formation, Carl Larson, who in addition to football also practiced athletics and wrestling, claimed the reason was that the main sports club in the city, Borås Athletic and Sports Society, would not exert football in their program.

Carl Larson, however, found that there were too many clubs containing the city name Borås which contributed to the name change in 1906 by Riksidrottsförbundet to the current, IF Elfsborg. The name is derived from Älvsborg County where instead of making use of the modern spelling Älvsborg, they used the older spelling with an E. The same goes for the club colours, reflected in their crest and kit, yellow and black. Colours that are taken from Älvsborg Regiment, Elfsborg would not only represent a city but a whole region. A recurring motto of the club is \"Vi Tillsammans\" (We together).

The club's homeground Borås Arena is also called Elfsborg Fortress, since Elfsborg is Allsvenskan home strongest team in the 2000s (decade). It is one of two teams in Allsvenskan that has won against the Sweden national team with 2–1 in the opening ceremony of Ryavallen (the other team is AIK 1979 with 3–2) and one of only two teams to win Allsvenskan as newcomers in 1961, the other team was Östers IF in 1968. Elfsborg have repeatedly participated for the qualifier to Champions League, Europa League and was as late as 2007 in 2007–08 UEFA Cup and was one of the co-winners in 2008 UEFA Intertoto Cup the following year.

The club have won six national championships, the latest in 2012, and three national cups.