The use of sulfur and selenium nucleophiles in organic and inorganic synthesis has been widely investigated. A broad range of functional group transformations can be accomplished by using nucleophilic chalcogen reagents. Additionally, biologically and synthetically valuable sulfur- and selenium-containing compounds have been prepared by using such nucleophilic species. The synthesis and the reactivity of nucleophilic sulfur and selenium reagents have already been reviewed in books and book chapters.^1,2  Metal thiolates and selenolates, which represent the commonly employed chalcogen nucleophilic reagents, have been comprehensively discussed therein. This chapter will focus on “unconventional” nucleophilic sulfur and selenium reagents containing chalcogen–boron, chalcogen–aluminium, chalcogen–silicon, and chalcogen–tin bonds. Features of the synthesis and reactivity of such species will be presented with particular emphasis on recent advances in the field, surveying the literature between 2000 and 2021.