After the terrorist attacks on the United States in 2001, the Firearms and Toolmarks Unit of the Federal Bureau of Investigation (FBI) Laboratory began collecting small and easily concealed knives. This report contains specific information on the manufacturer, composition, and a descriptive note and picture of each of the concealed weapons listed. The visual shown includes an accompanying scale for size, and include an X-ray photograph to show where the weapons might appear when concealed. In collecting and distributing information on concealed knives, it was found that many of the knives in the collection are commercially purchased, are common items found in most homes and offices, are made of plastic material, and are designed to cut. All the knives in this collection are considered to be and should be treated as potentially dangerous weapons.