I typically see Procurement as a subset of supply chain management (SCM).

Supply Chain Management is the active management of supply chain activities to maximize customer value and achieve sustainable competitive advantage. It represents a conscious effort by the supply chain firms to develop and run supply chains in the most effective & efficient ways possible. Supply chain activities cover everything from product development, sourcing, production, and logistics, as well as the information systems needed to coordinate these activities.

The concept of Supply Chain Management (SCM) is based on two core ideas:
1. The first is that practically every product that reaches an end-user represents the cumulative effort of multiple organizations. These organizations are referred to collectively as the supply chain.

2. The second idea is that while supply chains have existed for a long time, most organizations have only paid attention to what was happening within their “four walls.” Few businesses understood, much less managed, the entire chain of activities that ultimately delivered products to the final customer. The result was disjointed and often ineffective supply chains.

The organizations that make up the supply chain are “linked” together through physical flows and information flows.

Physical Flows
Physical flows involve the transformation, movement, and storage of goods and materials. They are the most visible piece of the supply chain. But just as important are information flows.

Information Flows
Information flows allow the various supply chain partners to coordinate their long-term plans, and to control the day-to-day flow of goods and materials up and down the supply chain.

Purchasing is primarily concerned with the inbound side of product and service flows, which then forms part of the overall flow of goods and services in the end to end supply chain.