A staple cartridge for use with a surgical stapler, said staple cartridge comprising: a cartridge body, comprising: a deck; and a plurality of staple cavities defined within said deck, wherein each said staple cavity comprises an opening in said deck; an implantable compressible portion, wherein said deck is positioned relative to a first side of said implantable compressible portion; a plurality of staples, wherein at least a portion of each said staple is removably stored within a said staple cavity; a plurality of staple drivers, each supporting one or more staples within the staple cavities, wherein the staples and the staple drivers are in unfired positions; a staple-firing sled which can be moved from a proximal end to a distal end of the staple cartridge to sequentially lift the staple drivers and the staples from their unfired positions to fired positions; wherein each said staple is deformable between an unfired configuration and a fired configuration when each said staple is moved between its unfired position and its fired position, and wherein said compressible portion is configured to be captured within said staples and may assume different compressed heights within different said staples when said staples are deformed between said unfired configuration and said fired configuration; and characterized in that each said staple extends above said deck and is at least partially positioned within said compressible portion, and that said cartridge comprises retaining means that receive and retain at least a portion of said staples prior to said staples being deployed from their unfired position to their fired position, wherein said implantable compressible portion is positioned intermediate said retaining means and said deck. a cartridge body, comprising: a deck; and a plurality of staple cavities defined within said deck, wherein each said staple cavity comprises an opening in said deck; a deck; and a plurality of staple cavities defined within said deck, wherein each said staple cavity comprises an opening in said deck; an implantable compressible portion, wherein said deck is positioned relative to a first side of said implantable compressible portion; a plurality of staples, wherein at least a portion of each said staple is removably stored within a said staple cavity; a plurality of staple drivers, each supporting one or more staples within the staple cavities, wherein the staples and the staple drivers are in unfired positions; a staple-firing sled which can be moved from a proximal end to a distal end of the staple cartridge to sequentially lift the staple drivers and the staples from their unfired positions to fired positions; wherein each said staple is deformable between an unfired configuration and a fired configuration when each said staple is moved between its unfired position and its fired position, and wherein said compressible portion is configured to be captured within said staples and may assume different compressed heights within different said staples when said staples are deformed between said unfired configuration and said fired configuration; and characterized in that each said staple extends above said deck and is at least partially positioned within said compressible portion, and that said cartridge comprises retaining means that receive and retain at least a portion of said staples prior to said staples being deployed from their unfired position to their fired position, wherein said implantable compressible portion is positioned intermediate said retaining means and said deck.