Sclerotinia is one of the most devastating and cosmopolitan plant pathogens with a broad host range. Sclerotinia includes 109 morphological species documented in the Index Fungorum and 15 species supported by molecular data. Numerous terms have been employed to describe diseases caused by Sclerotinia species, including cottony rot, watery soft rot, stem rot, drop, crown rot, blossom blight, and, most frequently, white mold. Sclerotinia sclerotiorum, the commonly reported species with significant economic impact, has been reported in Europe, Asia, Africa, North America, Central America, the Caribbean, and Oceania. Sclerotinia species are persistent soilborne fungi that exist as either mycelium or sclerotia and are spread primarily through mechanical transmission. Sclerotinia is composed mainly of necrotrophs, producing the characteristic resistant sclerotia over its life cycle. This multi-hyphal structure can remain viable over years of being dormant. Diseases caused by Sclerotinia species can cause significant yield losses. Precise and rapid detection and identification of Sclerotinia species are essential for effective disease management and mitigation. This chapter discusses current knowledge of Sclerotinia species, their associated diseases, biology, epidemiology, and their current management. This chapter also provides an updated phylogenetic tree based on multi-locus phylogenetic analyses of combined CaM, ITS, and Mcm7 datasets.