Chitin is primarily sourced from the exoskeletons of crustaceans, insects, arachnids and fungal cell walls Chitin is a natural polysaccharide made up of β-1,4-N-acetyl-D-glucosamine sugar molecules. Chitosan is produced by the enzymatic or chemical deacetylation of chitin. Further enzymatic, chemical and physical breakdown of chitosan yields chitooligosaccharides. Chitin and its derivatives have a broad range of applications due to their beneficial properties. Chitin and its derivatives play a role in both basal and specific plant defence systems. Exposure to chitin results in the plants adding extra layers of lignin and callose. Chitin and its derivatives structural similarity to compounds found in plant pathogens elicit specific plant defence responses which are more potent and enduring. Artificial chitosan films can act as antitranspirants and wound sealants when applied to plants. Additionally, chitin can act as a soil amendment as well as a fertilizer supplement. The cationic groups in the chitosan backbone confers antimicrobial activity, making it effective against plant pathogens. Although chitin and chitosan are not directly produced in plants, this chapter focuses on their multifunctionality and eco-friendly nature which makes them suitable for a wide range of applications as plant biostimulants. Emphasis is on plant growth enhancement, productivity and inhibition of pathogens.