The Federal Acquisition Streamlining Act (FASA) of 1994 is intended to simplify government buying procedures. It removed many competition restrictions on government purchases of less than $100,000. Instead of full and open competition, agencies can now use simplified procedures for soliciting and evaluating bids up to $100,000. Government agencies, however, are still required to advertise all planned purchases over $25,000 in www.FedBizOpps.gov.
Simplified procedures require fewer administrative details, lower approval levels, and less documentation. New procurement reform legislation requires all federal purchases above $2,500 but under $100,000 to be reserved for small businesses, unless the contracting officer cannot obtain offers from two or more small businesses that are competitive on price, quality and delivery.
Government purchases of up to $2,500 in individual items or multiple items whose aggregate amount does not exceed $2,500 are now classified as "micro-purchases" and can be made without obtaining competitive quotes. However, these purchases are no longer reserved for small businesses. Agencies can make micro-purchases using a Government Purchase Card (typical credit card).
Here is more specific information about government contracting process:
Information courtesy of the Small Business Administration.