What purchasing methods / contracts does the government use?

The Federal government utilizes a variety of different contract types depending on what it is buying, what funding is available, what the needs are and other factors. The trend is towards longer commitments and increased flexibility.

In general:

For micro purchases, under $25,000, a credit card is the preferred method of purchase and competition in most cases is not required.

Requirements under $100,000 are set aside for small business

The Federal Acquisition Regulations (FAR) Part 16 provides detailed information on contract types used by the Federal government. Refer to http://www.acquisition.gov/far/current/html/FARTOCP16.html

The General Services Administration (GSA) uses a contracting vehicle referred to as a GSA Schedules (also referred to as Multiple Award Schedules and Federal Supply Schedules). A schedule creates a long-term, government-wide contract with a commercial firm. More information on GSA schedules is available at http://www.gsa.gov/schedules