The laser conditioning of dielectric thin film HR coatings has been studied as a practical method for the improvement of the damage thresholds of large area (1.1 m dia.) high power 1064 nm laser mirrors on the LLNL 120 kJ, 100 TW Nova laser system. Both HfO₂/SiO₂ and ZrO₂/SiO₂HR coatings were conditioned by rastering with a small (∼0.2 mm) diameter beam from a pulsed (18 Hz, 8 ns) Nd-YAG laser (1064 nm). The samples were rastered at various fluences below the unconditioned damage threshold and subsequently damage tested. Large area conditioning studies were also performed using a large aperture beam of the Nova laser. The laser conditioning effect was found to be permanent. Improvements in damage threshold due to conditioning were as high as a factor of 2.7 and were dependent on the conditioning parameters. A model for the conditioning effect is proposed based on the emptying of electronic defect levels within the bandgap of the dielectric materials.