A device (1, 16, 26) for fastening tissue, comprising: a single closed ring (2, 17, 27) having an essentially planar configuration and an essentially cylindrical configuration, wherein the ring is elastically deformable and is suitable to be changed from the essentially planar configuration to the essentially cylindrical configuration by application of torsional energy, the ring having one or more tissue engaging projections (12, 22, 32) and being formed of multiple functional zones each extending along part of the circumference of the ring, the functional zones comprising: a) a plurality of twistable zones (11A, 11D, 21A, 31A), each of the twistable zones being capable of sustaining a 90 degree or more torsional rotation; b) one or more central zones (10, 20, 30) each tissue engaging projection extending from a central zone, each central zone including a central spine having a tissue-engaging projection (12, 22, 32) and a stabilizing projection (14, 24, 34), each central zone being connected to a pair of the twistable zones at the central spine by way of central zone junctions, the tissue-engaging projection projecting from one side of the ring approximately normally to a middle a plane of the ring when in the essentially cylindrical configuration, and the stabilizing projection projecting from an opposite side of the ring approximately normally to said plane of the ring when in the essentially cylindrical configuration, each stabilizing projection extending beyond any interconnection to a twistable zone; and c) one or more interconnecting zones (11B, 11C, 21B, 31B), each interconnecting zone being connected to a pair of the twistable zones; wherein reorientation of each tissue-engaging projection of the device to engage tissue, from the essentially cylindrical configuration of the ring to the essentially planar configuration, is driven by torsional energy stored in the ring. a single closed ring (2, 17, 27) having an essentially planar configuration and an essentially cylindrical configuration, wherein the ring is elastically deformable and is suitable to be changed from the essentially planar configuration to the essentially cylindrical configuration by application of torsional energy, the ring having one or more tissue engaging projections (12, 22, 32) and being formed of multiple functional zones each extending along part of the circumference of the ring, the functional zones comprising: a) a plurality of twistable zones (11A, 11D, 21A, 31A), each of the twistable zones being capable of sustaining a 90 degree or more torsional rotation; b) one or more central zones (10, 20, 30) each tissue engaging projection extending from a central zone, each central zone including a central spine having a tissue-engaging projection (12, 22, 32) and a stabilizing projection (14, 24, 34), each central zone being connected to a pair of the twistable zones at the central spine by way of central zone junctions, the tissue-engaging projection projecting from one side of the ring approximately normally to a middle a plane of the ring when in the essentially cylindrical configuration, and the stabilizing projection projecting from an opposite side of the ring approximately normally to said plane of the ring when in the essentially cylindrical configuration, each stabilizing projection extending beyond any interconnection to a twistable zone; and c) one or more interconnecting zones (11B, 11C, 21B, 31B), each interconnecting zone being connected to a pair of the twistable zones; wherein reorientation of each tissue-engaging projection of the device to engage tissue, from the essentially cylindrical configuration of the ring to the essentially planar configuration, is driven by torsional energy stored in the ring. a) a plurality of twistable zones (11A, 11D, 21A, 31A), each of the twistable zones being capable of sustaining a 90 degree or more torsional rotation; b) one or more central zones (10, 20, 30) each tissue engaging projection extending from a central zone, each central zone including a central spine having a tissue-engaging projection (12, 22, 32) and a stabilizing projection (14, 24, 34), each central zone being connected to a pair of the twistable zones at the central spine by way of central zone junctions, the tissue-engaging projection projecting from one side of the ring approximately normally to a middle a plane of the ring when in the essentially cylindrical configuration, and the stabilizing projection projecting from an opposite side of the ring approximately normally to said plane of the ring when in the essentially cylindrical configuration, each stabilizing projection extending beyond any interconnection to a twistable zone; and c) one or more interconnecting zones (11B, 11C, 21B, 31B), each interconnecting zone being connected to a pair of the twistable zones;