The Eurasian blue tit (Cyanistes caeruleus) is a small passerine bird in the tit family Paridae. The bird is easily recognisable by its blue and yellow plumage.

Eurasian blue tits, usually resident and non-migratory birds, are widespread and a common resident breeder throughout temperate and subarctic Europe and western Asia in deciduous or mixed woodlands with a high proportion of oak. They usually nest in tree holes, although they easily adapt to nest boxes where necessary. Their main rival for nests and in the search for food is the larger great tit.