In the business to business direct marketing field there are three fundamental strategies. First, business marketers who sell consumables such as office supplies, medical supplies, or some business services through mail order need to rely on building a database and on back-end marketing to maintain profits, similar to consumer marketing. For many business marketers a second strategy is necessary. Many business and industrial products are so expensive or complex that they cannot be sold by mail order and require demonstrations or in-person sales calls. In this instance, direct marketing is used for lead generation, to identify and qualify prospects who can be contacted on the phone or in per-son later.