Bleeding disorders are a group of conditions that result when the blood cannot clot properly. In normal clotting, platelets, a type of blood cell, stick together and form a plug at the site of an injured blood vessel. Proteins in the blood called clotting factors then interact to form a fibrin clot, essentially a gel plug, which holds the platelets in place and allows healing to occur at the site of the injury while preventing blood from escaping the blood vessel. While too much clotting can lead to conditions such as heart attacks and strokes, the inability to form clots can be very dangerous as well, as it can result in excessive bleeding. Bleeding can result from either too few or abnormal platelets, abnormal or low amounts of clotting proteins, or abnormal blood vessels.

Hemophilia is perhaps the most well-known inherited bleeding disorder, although it is relatively rare. It affects mostly males. Many more people are affected by von Willebrand disease, the most common inherited bleeding disorder in some countries caused by clotting proteins. Von Willebrand disease can affect both males and females. Platelet disorders are the most common cause of bleeding disorder and are usually acquired rather than inherited.