A surgical stapler comprising: first and second jaw members (142, 144) moveable relative to one another between an open configuration and a clamped configuration, the first and second jaw members configured to clamp tissue therebetween in the clamped configuration, the first jaw member including an anvil and the second jaw member including a staple cartridge having a plurality of staples configured to be driven through the tissue clamped between the first and second jaw members, characterised by: the first jaw member including a surface opposing a surface of the second jaw member; an opening defined in the surface of the first jaw member; a light source configured to emit light from the opening; and a light detector disposed within the opening, the light detector configured to sense properties of light reflected off tissue clamped between the first and second jaw members and to generate signals indicative of the sensed properties of light; and a processor operatively associated with the light detector, the processor configured to: receive signals indicative of properties of light from the light detector; analyze the signals to determine an attribute of tissue clamped between the first and second jaw members; and provide feedback to a user of the attribute of tissue clamped between the first and second jaw member. first and second jaw members (142, 144) moveable relative to one another between an open configuration and a clamped configuration, the first and second jaw members configured to clamp tissue therebetween in the clamped configuration, the first jaw member including an anvil and the second jaw member including a staple cartridge having a plurality of staples configured to be driven through the tissue clamped between the first and second jaw members, characterised by: the first jaw member including the first jaw member including a surface opposing a surface of the second jaw member; an opening defined in the surface of the first jaw member; a light source configured to emit light from the opening; and a light detector disposed within the opening, the light detector configured to sense properties of light reflected off tissue clamped between the first and second jaw members and to generate signals indicative of the sensed properties of light; and a processor operatively associated with the light detector, the processor configured to: receive signals indicative of properties of light from the light detector; analyze the signals to determine an attribute of tissue clamped between the first and second jaw members; and provide feedback to a user of the attribute of tissue clamped between the first and second jaw member. an opening defined in the surface of the first jaw member; a light source configured to emit light from the opening; and a light detector disposed within the opening, the light detector configured to sense properties of light reflected off tissue clamped between the first and second jaw members and to generate signals indicative of the sensed properties of light; and a processor operatively associated with the light detector, the processor configured to: receive signals indicative of properties of light from the light detector; analyze the signals to determine an attribute of tissue clamped between the first and second jaw members; and provide feedback to a user of the attribute of tissue clamped between the first and second jaw member. receive signals indicative of properties of light from the light detector; analyze the signals to determine an attribute of tissue clamped between the first and second jaw members; and provide feedback to a user of the attribute of tissue clamped between the first and second jaw member.