Pinaceae and Podocarpaceae are the two most diverse families of conifers, but have strikingly different ecological and geographic ranges. Pinaceae are almost exclusively Northern Hemisphere. Podocarpaceae are widespread across the Southern Hemisphere but extend into the north, and even overlap with Pinaceae in several areas. This chapter investigates the ecology and history of these families, and how they led to the families’ current distributions. We use bioclimatic analyses combined with existing knowledge of phylogeny, fossil record, and physiology to argue that the patterns primarily derive from slow rates of evolution of functionally significant characteristics (evolutionary niche conservatism). The evidence indicates that very limited evolution of tolerance of frost and freezing climates have constrained the success of Podocarpaceae in the Northern Hemisphere, while evolution of traits allowing Pinaceae to compete with angiosperms in tropical rainforest has been very limited. Even Podocarpaceae, with their convergence towards the broad leaves and animal seed dispersal common in angiosperms, have little capacity to compete in lowland tropical rainforest. Important exceptions to these patterns demonstrate that, even though this conservatism has restricted the geography of the family for over tens of millions of years, it is not absolute. This evolutionary conservatism is stronger in precipitation-related dimensions of niches than in thermal dimensions, especially for Podocarpaceae. Although the tropically derived Podocarpaceae of the Northern Hemisphere have failed to colonise freezing climates, temperate Southern Hemisphere Podocarpaceae have evolved into most extreme freezing climates that are compatible with woody plant growth within that region. Dispersal limitations may play a secondary role: tropical rainforest may have provided too large a barrier for Pinaceae to disperse naturally into temperate Southern Hemisphere, and extensive deserts may have constrained the expansion of Podocarpaceae within the Northern Hemisphere.