An interspinous process spacer for implantation in an interspinous space between a superior spinous process and an inferior spinous process includes a balloon-like body, a first deployable protrusion and a second deployable protrusion. The body has a distal end, a proximal end and a longitudinal axis extending between the proximal and distal ends. The spacer is arrangeable in an unexpanded configuration and an expanded configuration. The first deployable protrusion is mounted proximate the proximal end and the second deployable protrusion is mounted proximate the distal end. The first and second deployable protrusions are oriented generally parallel to the longitudinal axis in the unexpanded configuration and generally perpendicular to the longitudinal axis in the expanded configuration.