Stropharia caerulea, commonly known as the blue roundhead, is a species of mushroom forming fungus in the family Strophariaceae. It is a somewhat common species found in Europe and North America, where it grows as a saprophyte in meadows, roadsides, hedgerows, gardens, and woodchip mulch. S. caerulea was officially described to science in 1979, although it was known to be a distinct species for about two centuries before that. The scientific name Stropharia cyanea, as defined by Tuomikoski in 1953, and used by several later authors, is a synonym of S. caerulea.

The fruit bodies (mushrooms) of Stropharia caerulea feature a greenish-blue cap sparsely covered in white flecks of veil at the margin, and a sticky, glutinous surface texture. Gills on the cap underside have an adnate or sinuate attachment to the stipe. They are initially pale purplish-brown, becoming darker brown in age as the spores mature. The greenish stipe is covered in white scales up to a thin, transient ring. It is similar in appearance to a less common relative Stropharia aeruginosa, but that species has a more robust ring on its stipe, more scales on the cap, and darker gills with white edges.

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