An "aftermarket" is a market for the supply of products or services needed for or in connection with the use of a relatively long-lasting piece of equipment that has already been acquired. Aftermarkets give rise to several kinds of questions under competition law. Does a relevant market for competitive analysis consist of separate markets for primary and secondary products, or is it a market for "systems" consisting of both primary and secondary products? When, if at all, is the supplier of the primary product dominant in the aftermarket for products or services needed for use with its equipment? If it is dominant, what conduct may be an abuse prohibited by Article 102 (ex-82) of what is now the Treaty on the Functioning of the European Union? This article applies well-known general principles of competition law, along with case law, to answer these questions.