Firearm Background Checks: Current Federal Framework and the House-Passed Proposals in the 116th Congress [Updated March 1, 2019] [open pdf - 415KB]
From the Document: "Federal law requires a background check for many, but not all, firearms transfers. The Brady Handgun Violence Prevention Act (Brady Act), Pub. L. No. 103-159, 107 Stat. 1536, established the federal framework for firearms background checks. Under the Act, the Federal Bureau of Investigation (FBI) established the National Instant Criminal Background Check System (NICS), which queries various government records that could reveal a prospective transferee is ineligible to receive a firearm. Since the Brady Act became law in 1993 and NICS went live in 1998, the framework governing the background check system has remained largely unchanged. Amendments to the Brady Act generally have addressed getting more records entered into the system by state and federal entities."
CRS Report for Congress, IF11121
Congressional Research Service: https://crsreports.congress.gov/