The present invention relates to an interspinous spacer (10, 10′, 10″, 10′″, 10″″, 10′″″) for implantation between adjacent spinous process (SP) to treat spinal stenosis. The interspinous spacer preferably includes a W-shaped or S-shaped leaf spring body member (21) for insertion between adjacent spinous processes and one or more wire straps (42) extending from the body to attach the spacer to the adjacent spinous processes. The wire straps are preferably sized and configured to extend from one side of the leaf spring, along one side of a spinous process, over or under the spinous process to the other side wherein the wire strap can be coupled to the leaf spring. Alternatively, the spacer may include one or more hooks (60) for engaging one or both of the adjacent spinous processes. Preferably, the top bone contacting surface (22) has a more accentuated convex shape compared to the bottom surface (24) so that the spacer is better able to sit in the naturally formed concavity present in the bottom surface of a spinous process.