A shape-changing anatomical anchor includes an activation means arranged to convert the anchor from a de-activated state to an activated state, and one or more members which extend away from the activation means and thereby change the shape of the anchor when the anchor is activated. The anchor is installed within bone and/or soft tissue when de-activated; when activated, the shape change acts to increase the force with which the anchor is retained within the tissue in which it is installed. Both piloted and non-piloted versions are described.