The applications of laser scanning systems in areas such as laser welding, cutting and marking continue to increase with the improvement in scanning mechanisms such as galvanometer scanners. These continue to challenge the optical designer to produce high performance lenses which can fulfill the need for a smaller focused spot size over larger flat field scan areas. CO<SUB>2</SUB> lasers offer the advantages of high power (kW) but their long wavelength of 10.6 microns compared to 1.06 microns of Nd-YAG means that CO<SUB>2</SUB> has 10 times the focussed spot size for the same aperture. Increasing the aperture of CO<SUB>2</SUB> scanning systems will therefore help to increase the application potential of these systems. This paper presents a review of the optical design factors which determine the performance of a CO<SUB>2</SUB> scanning system. These factors have been used to produce several lens designs which are capable of scanning a focussed spot size of 100 microns or less over areas up to 100 mm square.