Surface ozone records from ten polar research stations were investigated for the dependencies of ozone on radiative processes, snow-photochemisty, and synoptic and stratospheric transport. A total of 146 annual data records for the Arctic sites Barrow, Alaska; Summit, Greenland; Alert, Canada; Zeppelinfjellet, Norway; and the Antarctic stations Halley, McMurdo, Neumayer, Sanae, Syowa, and South Pole were analyzed. Mean ozone at the Northern Hemisphere (NH) stations (excluding Summit) is 5 ppbv higher than in Antarctica. Statistical analysis yielded best estimates for the projected year 2005 median annual ozone mixing ratios, which for the Arctic stations were 33.5 ppbv at Alert, 28.6 ppbv at Barrow, 46.3 ppbv ppb at Summit and 33.7 ppbv at Zeppelinfjellet. For the Antarctic stations the corresponding ozone mixing ratios were 21.6 ppbv at Halley, 27.0 ppbv at McMurdo, 24.9 ppbv at Neumayer, 27.2 ppbv at Sanae, 29.4 ppbv at South Pole, and 25.8 ppbv at Syowa. At both Summit (3212 m asl) and South Pole (2830 m asl), annual mean ozone is higher than at the lower elevation and coastal stations. A trend analysis revealed that all sites in recent years have experienced low to moderate increases in surface ozone ranging from 0.02 to 0.26 ppbv yr−1, albeit none of these changes were found to be statistically significant trends. A seasonal trend analysis showed above-average increases in ozone during the spring and early summer periods for both Arctic (Alert, Zeppelinfjellet) and Antarctic (McMurdo, Neumayer, South Pole) sites. In contrast, at Barrow, springtime ozone has been declining. All coastal stations experience springtime episodes with rapid depletion of ozone in the boundary layer, attributable to photochemically catalyzed ozone depletion from halogen chemistry. This effect is most obvious at Barrow, followed by Alert. Springtime depletion episodes are less pronounced at Antarctic stations. At South Pole, during the Antarctic spring and summer, photochemical ozone production yields frequent episodes with enhanced surface ozone. Other Antarctic stations show similar, though less frequent spring and summertime periods with enhanced ozone. The Antarctic data provide evidence that austral spring and summertime ozone production in Antarctica is widespread, respectively, affects all stations at least through transport events. This ozone production contributes to a several ppbv enhancement in the annual mean ozone over the Antarctic plateau; however, it is not the determining process in the Antarctic seasonal ozone cycle. Although Summit and South Pole have many similarities in their environmental conditions, this ozone production does not appear to be of equal importance at Summit. Amplitudes of diurnal, summertime ozone cycles at these polar sites are weaker than at lower latitude locations. Amplitudes of seasonal ozone changes are larger in the Southern Hemisphere (by 5 ppbv), most likely due to less summertime photochemical ozone loss and more transport of ozone-rich air to the Arctic during the NH spring and summer months.