Abstract: A ring binder mechanism comprises a fixed part (10) for mounting on a folder, and a movable part (13) connected to the fixed part by a four-bar-chain linkage (15) allowing translational movement of the movable part relatively to the fixed part between an open position and a closed position. The movable part (13) is also connected to the fixed part (10) by a pair of resiliently deformable links (17) which provide a spring-loaded over-center device. Two pairs of paper-holding elements (18, 21) are provided, the elements of each pair being separated in the open position of the movable part (13) but being brought into engagement with one another in the closed position, so as to prevent removal of sheets of paper threaded thereon. The fixed part (10), the movable part (13), the paper-holding elements (18, 21), the four-bar-chain (15), and the over-center device (17) are integrally formed with one another as parts of a single plastics moulding.