The role of a purchasing department is to procure goods and services for an organization; thus, it's also referred to as the procurement department. Companies, universities and governments all have this division to make purchasing decisions on their behalf.
The department is a cost optimizer, always looking for ways to secure the best deal from suppliers. However, it's not just looking for low cost; it's also looking for high quality and service guarantees.
Purchasing departments generally solicit bids from potential vendors by putting out a request for quotes, or RFQ. The RFQ will specify in detail the department's requirements. Vendors are given a time frame to respond within, along with their cost quote to fulfill the requirements.