BRs (Brassinosteroids) are Plant Steroid Hormones that influence a wide range of important Developmental and Physiological processes, including Regulation of Gene Expression, Cell Division and Expansion, Differentiation, Programmed Cell Death, and Homeostasis. The regulation of these processes by BRs, acting together with other plant hormones, leads to the promotion of Stem Elongation and Pollen tube Growth, Leaf Bending and Epinasty, Root Growth Inhibition, Proton-Pump Activation, and Xylem Differentiation. The pathways of BR biosynthesis have been elucidated by a series of detailed biochemical studies. The biosynthetic pathway to BL (Brassinolide), the biologically most active BR, can be divided into General Sterol Synthesis (Cycloartenol to Campesterol), and the BR-Specific Pathway from Campesterol to BL. BL is a polyhydroxylated derivative of 5-Alpha-Cholestan, namely [...]