This book reviews the chemical structure, biosynthesis and function of insect juvenile hormone (JH). JH possesses a unique sesquiterpenoid structure that is uncommon among animal hormones. Since Sir Vincent Wigglesworth first reported the function of JH using an insect of Heteroptera in 1934, its structure and properties have long attracted the attention of many insect physiologists. Moreover, its unique chemical structure and biosynthetic process have led to the expectation that it could be developed for applications such as pest control. Starting from the history of JH research, this book covers its chemical structure, biosynthesis, functions, and applications. The book focuses on the findings that have been clarified in recent years, such as the chemical structure, the biosynthetic processes, receptors and molecular and cellular mechanisms regulating various physiological functions in JH, while also referring to the classical properties of the hormone. The book also emphasizes applied research, exploring the potential of new insecticides and examining the impact of JH on environmental responses. With contributions from international experts, the book culminates the 90 years of JH research, highlighting the contributions of the Japanese research community to its advancement and its global significance. The editors are the leading researchers who first found the key enzyme in the JH biosynthesis and determined the chemical structure of the JH specific to Heteroptera. Target audiences are researchers and graduate students in biological sciences, especially insect endocrinology and molecular biology. Industry professionals and those interested in environmental science and applied ecology may also find this book of interest.