Atmospheric fronts in the lower troposphere often mark regions of significant weather and serve as an important conceptual tool that is frequently used and well understood by the public. This study uses an objective method to identify fronts in the ERA-40 reanalysis and to compile a quantitative global climatology of their occurrence. The climatology confirms the mid-latitude storm tracks as the regions of highest front frequency and identifies slow moving frontal boundaries in the subtropics corresponding to major climate features, such as the Mei-Yu front. The climatology also shows fronts to be common features of the South Pacific convergence zone. In the northern hemisphere fronts shift poleward in summer. In the southern hemisphere this and other aspects of seasonal behavior are rather different.