Marketing describes both the organisational function and the process concerned with identifying, anticipating and satisfying customer requirements profitably. Sales activities are often described as the mirror image of purchasing, and marketing activities as the mirror image of procurement. Both functions are concerned with identifying opportunities to create, claim and/or share value. Most marketing texts still describe largely passive buyers responding to proactive marketing strategies, and the key change for many business-to-business marketing practitioners is that a procurement process driven by the client has superseded the sales process driven by the seller.