This review covers all known terpenoids containing an unsaturated 1,4-dialdehyde (3-formyl-3-butenal) functionality that have been isolated from natural sources. The structures (Figures 1-5) and sources (Table 1) are given, and their biological activities, the ways that the producing organisms handle the unsaturated dialdehydes, as well as their chemical reactivity as electrophiles is discussed. In addition, a summary of the possible applications of unsaturated dialdehydes is given.