AbstractThis chapter provides an overview of plant antimicrobial peptides. It mainly focuses on one particular class of plant defence peptides, namely the cyclotides, which have been discovered over the last decade in plants from the Rubiaceae, Violaceae and Cucurbitaceae families. Cyclotides have a head-to-tail cyclized peptide backbone and a cystine knot motif formed from their six conserved cysteine residues, which makes them exceptionally stable. This chapter describes their isolation and characterization, structure and biosynthesis, and applications. The structural stability of cyclotides makes them excellent scaffolds for the engineering of novel therapeutic proteins. Advances in methods for the production of cyclotides and their potential clinical applications are also described.