The paper defines an "assault weapon" as a "civilian, semiautomatic version of a military weapon." Generally, the characteristics of an assault weapon make firearms more lethal, more accurate, and/or less conspicuous when used. Federal and State laws also establish specific definitions of an "assault weapon" for the purposes of regulation. Data are provided on the ownership of assault weapons in the United States prior to the 1994 ban on such weapons, as well as the use of assault weapons in crime before the Federal ban. Information on law enforcement officers killed by assault weapons indicates that between January 1, 1994, and September 30, 1995, 33 law enforcement officers were killed with an assault weapon (n=16) or other weapon sold with large-capacity magazines (n=17) affected by the 1994 Federal assault weapons ban. Regarding assault weapon injuries, this report notes that although assault weapons currently account for a relatively small proportion of crime guns, these weapons are designed for highly lethal assaults. Information on public opinion shows that national surveys conducted in 2000 and 2002 indicate that between 67 percent and 71 percent of adults favor the current Federal ban on assault weapons, and 65 percent of registered voters favor renewal of the 1994 ban. This report also provides information on Federal and State laws that ban assault weapons, the effectiveness of assault weapons bans, and the manufacture and sale of "copycat" weapons. A 1999 study that evaluated the effects of the 1994 Federal assault weapons ban found a 20-percent decrease (from 4,077 in 1994 to 3,268 in 1995) in the criminal use (and police confiscation) of assault weapons in the first year of the ban. This decline was twice as large as the overall reduction in crime gun trace requests. 20 references