Anchors, anchoring systems, anchor delivery devices, and method of using anchors are described. An anchor may be a flexible anchor having two curved legs that cross in a single turning direction to form a loop, wherein the legs are adapted to penetrate tissue. The ends of the curved legs may be blunt or sharp. The anchor can assume different configurations such as a deployed configuration and a delivery configuration, and the anchor may switch between these different configurations. In operation, the anchor may be inserted into tissue by releasing the anchor from a delivery configuration so that the anchor self-expands into the deployed configuration, so that the legs of the anchor may penetrate the tissue in a curved pathway.