Beyond that, the thoroughness of a background check depends on the employer. At a minimum, an employer will verify your Social Security number, pull your credit report and search driving and criminal records. They'll also verify that you went to school and worked at the places that you listed on your resume.
More extensive investigations reveal civil suits and judgments, accounts that go to collection and unpaid tax liens. A growing number of employers also look at Facebook profiles to see if you have posted offensive comments and photos - or what others have said about you online. For top-level hires, investigators may even interview neighbors and associates.
Many businesses, big and small, rely on companies that specialize in background checks to guide them through the process. Reputable firms follow standards set by the Fair Credit Reporting Act.