Ligament, in anatomy, tough band of slightly elastic connective tissue, made of a fibrous protein known as collagen.

One type of ligament, such as a collateral ligament of the elbow or knee, holds together bones and cartilage at a joint. This white, shiny ligament provides flexibility for freedom of movement and, at the same time, prevents the bones from moving too far apart.

Another type of ligament is thickened tissue that surrounds and directly reinforces a joint, such as the shoulder and hip. Ligaments of yellow elastic tissue connect adjoining vertebrae in the spine.

Ligaments also support abdominal organs, such as the liver, kidneys, spleen, bladder, uterus, and diaphragm, and help maintain the shape of the breasts. These ligaments are extensions of membranes covering the organs, or sheets of fibrous tissue.

Persistent stress or sudden, extreme flexing of a joint can cause a ligament to be stretched too far, resulting in injury. An example of severe ligament damage is a torn anterior cruciate ligament, the major ligament connecting bones in the knee joint—a relatively common athletic injury.