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In the area of contraception, especially combined oral contraceptives (COCs), ethinyl oestradiol (EE) has been the clear market leader for many decades. This chapter sets out the rather peculiar background to the inclusion of oestrogens in contraception as well as reviews some simple pharmacology. The classic mechanism of action for all steroid hormones is to bind to specific intracellular receptors and induce change in their shape, encouraging dimerization (two pairs of hormone/receptor complexes forming a single unit) and leading to recruitment of co-regulators. The complexes formed through this route are able to influence gene transcription and hence the production of proteins with biological activities. Until the last few years a prescriber discussing contraceptive options with a woman could bring in issues such as the route of administration of contraceptive steroids, their doses and dosing schedules and the type of progestogen.