Guanidines and biguanides are strong bases which are convenient to use as catalysts due to their solubility in organic media; as their basicities are in the range of the common inorganic bases such as alkaline hydroxides and carbonates, they are suitable for st wide range of base- directed reactions such as Michael addition, esterification and transesterification. New syntheses of poly-IV-alkylated biguanides have been devised from carbodiimides and recent examples of catalyses with soluble and immobilised guanidines and biguanides are given with emphasis on the transesterification of triglycerides from vegetable oils.