The catalyzed addition of distannanes, silylstannanes, borastannes, and borasilanes to unsaturated organic molecules is reviewed, with an emphasis on the scope of substrates and catalysts and synthetically useful transformations. Reactions include additions to alkenes, allenes, alkynes as well as to molecules containing combinations of these functional groups. Examples for further transformation of the resulting organic products are given. Issues of regioselectivity and diastereoselectivty in the additions are discussed in the context of catalyst choice as are differences seen in the addition of various element–element bonds to given substrates.