The femur or thigh bone, is the most proximal (closest to the hip joint) bone of the leg in tetrapod vertebrates capable of walking or jumping.

The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia and kneecap forming the knee joint. By most measures the femur is the strongest bone in the body. The femur is also the longest bone in the body.