AbstractCofactors are non‐protein entities necessary for proteins to operate. They provide “functional groups” beyond those of the 20 canonical amino acids and enable proteins to carry out more diverse functions. Such a viewpoint is rarely mentioned, if at all, when it comes to natural products and is the theme of this Concept. Even though the mechanisms of action (MOA) of only a few natural products are known to require cofactors, we believe that cofactor mediated MOA in natural products are far more prevalent than what we currently know. Bleomycin is a case in point. It binds iron cation to form a pseudoenzyme that generates reactive oxygen species. As another example, calcium cations induce laspartomycin to “fold” into the active conformation. Iron and calcium are bona fide cofactors for bleomycin and laspartomycin, respectively, as these natural products do not display their characteristic anticancer and antibacterial activities without Fe(II) and Ca(II). These types of cofactor mediated MOA in natural products were discovered mostly serendipitously, and being conscious of such a possibility is the first step toward identifying more novel chemistry that nature performs.