Poecile is a genus of birds in the tit family Paridae. It contains 15 species, which are scattered across North America, Europe and Asia; the North American species are the chickadees. In the past, most authorities retained Poecile as a subgenus within the genus Parus, but treatment as a distinct genus, initiated by the American Ornithologists Union, is now widely accepted. This is supported by mtDNA cytochrome b sequence analysis.

The marsh tit is a Eurasian passerine bird in the tit family Paridae and genus Poecile, closely related to the willow tit, Père David's and Songar tits. It is a small bird, around 12 cm (4.7 in) long and weighing 12 g (0.42 oz), with a black crown and nape, pale cheeks, brown back and greyish-brown wings and tail. Between 8 and 11 subspecies are recognised. Its close resemblance to the willow tit can cause identification problems, especially in the United Kingdom where the local subspecies of the two are very similar: they were not recognised as separate species until 1897.