A fastener for sheet objects comprising: first and second portions (3, 4), optionally formed as a unitary body, which are positioned or are positionable in an adjacent spaced relationship with respect to each other so as to define a sheet object receiving region therebetween; piercing means mounted on the first portion for piercing said one or more sheet objects, the piercing means being adapted so as to pierce one or more sheet objects disposed within the sheet object receiving region when moved into an operative state in which the piercing means extends across the sheet object receiving region between the first and second portions (3, 4); and retaining means for retaining the piercing means in the operative state when moved thereto, characterised in that the piercing means comprise a pin member with a pointed end, that the pin member is mounted on the first portion so as to be movable with respect thereto, that the pin member is coupled to an operating member comprising a button portion adapted for manipulation by a user, that the operating member includes two legs (17, 18) which are adapted to fold and biasing means for biasing the operating member towards an initial state in which the piercing means does not extend across the sheet object receiving region and that the retaining means comprises a pin-receiving member disposed on the second portion, the pin-receiving member comprising an aperture for receiving the pin member therein, the aperture being disposed in the centre of a disc forming part of the pin-receiving member, the pin-receiving member comprising a plurality of, preferably linear, radial slots extending from the aperture towards the circumference of the disc. first and second portions (3, 4), optionally formed as a unitary body, which are positioned or are positionable in an adjacent spaced relationship with respect to each other so as to define a sheet object receiving region therebetween; piercing means mounted on the first portion for piercing said one or more sheet objects, the piercing means being adapted so as to pierce one or more sheet objects disposed within the sheet object receiving region when moved into an operative state in which the piercing means extends across the sheet object receiving region between the first and second portions (3, 4); and retaining means for retaining the piercing means in the operative state when moved thereto, characterised in that the piercing means comprise a pin member with a pointed end, that the pin member is mounted on the first portion so as to be movable with respect thereto, that the pin member is coupled to an operating member comprising a button portion adapted for manipulation by a user, that the operating member includes two legs (17, 18) which are adapted to fold and biasing means for biasing the operating member towards an initial state in which the piercing means does not extend across the sheet object receiving region and that the retaining means comprises a pin-receiving member disposed on the second portion, the pin-receiving member comprising an aperture for receiving the pin member therein, the aperture being disposed in the centre of a disc forming part of the pin-receiving member, the pin-receiving member comprising a plurality of, preferably linear, radial slots extending from the aperture towards the circumference of the disc.