The degradation of fatty acids in plants occurs primarily in the peroxisomes through the β-oxidation cycle. Enzymes that are involved in various aspects of β-oxidation have been identified recently and shown to act biochemically on a diversity of fatty acids and derivatives. Analysis of several mutants has revealed essential roles for β-oxidation in the breakdown of reserve triacylglycerols, seed development, seed germination and post-germinative growth before the establishment of photosynthesis. β-Oxidation has also a considerable importance during the vegetative and reproductive growth phases, and plays a role in plant responses to stress, particularly in the synthesis of jasmonic acid.