Celery is a commercially important seed spice belonging to the family Umbelliferrae. Celery is used in various forms such as fresh herb, stalk, seeds, oil, and oleoresin for flavoring of foods and for medicinal purposes. Celery seed contains 2% volatile oil that finds application for flavoring of foods and also in perfumery industry. Limonene and selinene form about 60% and 20% of the oil, respectively. However, the important flavor constituents of the oil responsible for the typical aroma are 3-n-butyl-4-5-dihydrophthalide (sedanenolide), 3-n-butyl phthalide, sedanolide, and sedanonic anhydride present in very low levels (1-3%). Celery contains 15% fatty oil with the fatty acids: petroselenic (64.3%), oleic (8.1%), linoleic (18%), linolenic (0.6%), and palmitic acids. Phthalides especially sedanenaloide possess many health benefits. Celery extracts are reported to possess many nutraceutical properties, viz., antioxidant, hypolipidemic, hypoglycemic, and anti-platelet aggregation. In the present review, the chemistry, processing, and biological activities of celery and the components responsible are discussed.