Bog heather (often called "cross-leaved heath") is a species of heather found in Atlantic areas of Europe, from southern Portugal to central Norway, as well as a number of boggy regions further from the coast in Central Europe. In bogs, wet heaths and damp coniferous woodland, Erica tetralix can become a dominant part of the flora. It has also been introduced to parts of North America and other parts of Europe such as Austria and Switzerland.

It is a perennial subshrub with small pink bell-shaped drooping flowers borne in compact clusters at the ends of its shoots, and leaves in whorls of four (whence the name). The flowers appear between June and October, and can be distinguished from those of other European members of the genus Erica by the lack of protruding anthers. The distinction between Bog heather (E. tetralix) and the related Heather (genus Calluna) is by the leaves, which are small and scale-like in Calluna, but linear in Erica.