A Synovial joint, also known as a diarthrosis, is the most common and most movable type of joint in the body of a mammal. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones.

Structural and functional differences distinguish synovial joints from cartilaginous joints (synchondroses and symphyses) and fibrous joints (sutures, gomphoses, and syndesmoses). The main structural differences between synovial and fibrous joints are the existence of capsules surrounding the articulating surfaces of a synovial joint and the presence of lubricating synovial fluid within those capsules (synovial cavities).

Synovial joints contain the following structures:

Many diarthroses also contain:

The bone surrounding the joint on the proximal side is sometimes called the plafond, especially in the talocrural joint. A damage to this occurs in a Gosselin fracture.

The blood supply of a synovial joint is derived from the arteries sharing in the anastomosis around the joint.