The classification of lipids as steroids restricts family members to products of cholesterol biosynthesis from the cyclization of 2,3-oxidosqualene to various metabolic products with a tetracyclic perhydrophenanthrylenyl basic structural unit. Even so, a large number of very important lipids are included in this designation that serve very diverse roles in biochemistry and physiology. This chapter looks at cholesterols, estrogens, androgens, testosterone and dehydroepiandrosterone sulphate, adrenocorticosteroids and progestins, secosteroids, bile acids and steroid sulphate conjugates.