Strigolactones (SLs) are carotenoid-derived plant terpenes which function in the rhizosphere and in planta. In the rhizosphere, SLs induce seed germination in root parasitic plants and hyphal branching in arbuscular mycorrhizal (AM) fungi, therefore mediating both parasitic and symbiotic interactions with SL-producing plants and root parasitic plants and AM fungi, respectively. In planta, SLs are a group of plant hormones regulating plant growth and development through crosstalk with other hormones. In this chapter, chemistry, biosynthesis and its regulation, analytical methods, and biological functions of SLs are discussed along with their potential agronomical uses.