The chemical structure of juvenile hormone (JH) was first determined in 1967, nearly three decades after the discovery of the “inhibitory factor” that inhibited metamorphosis of the blood-sucking bug Rhodnius prolixus. Since then, it took almost half a century to identify JH occurring in Hemiptera, including this important model insect. This chapter summarizes the history of JH chemistry, along with related chemicals. The finding that “Golden oil,” extracts of the abdomen of Cecropia male moths, contained a large amount of JH activity was a breakthrough for the structure determination of JH I. Following this success, a group of epoxides of methyl farnesoate (MF) was described as insect JHs, and the structure of the Hemiptera-specific JH, JH III skipped bisepoxide (JHSB3), was finally determined in 2009. Because MF was shown to be a JH equivalent in Decapoda, Crustacea, it was likely to be the simplest form of JH. MF was then modified to 10,11-epoxide, JH III, which was known to be most widespread among insects. This structure was further diversified in an order-specific manner. Many questions about JH chemistry are unanswered yet, and efforts to answer these questions will open new avenues for advancing JH research and its potential applications.