Publisher Summary This chapter discusses the juvenile hormones (JH). The JH, a family of acyclic sesquiterpenoids, are essential to insect development and reproduction. This chapter examines the new compounds that have been added to the family. Recent structural elucidation of the hemolymph transport and catabolic proteins is examined. Molecular biology surrounding the long-sought JH receptor and potential candidates are discussed. The juvenile hormones, a family of acyclic sesquiterpenoids, are essential to insect development and reproduction. This family of hormones has been extensively studied because of its central role in regulating development and value as an insect pest control agent. Recent advances have been made in the areas of chemistry, biosynthesis, transport, catabolism, and biological roles the hormones play in the immature insect. Two common features characterize the naturally occurring JHs: their site of synthesis, the corpora allata (CA), and their farnesoid structure.