The variability in subduction styles along the Andean margin is investigated with regard to its probable causes and likely effects. It is shown that there is no single Andean or Chilean subduction style. The alternation of segments of flat-slab subduction and steep subduction argue against mechanisms involving continental scale boundary conditions. The best candidate for explaining flat subduction style appears to be buoyancy related to thickened oceanic crust of moderate to young age. A high degree of interplate coupling and great subduction zone earthquakes can occur along both flat-slab segments and steeply subducting segments. In general interplate coupling is higher for flat-slab segments as demonstrated by a statistical analysis of deformation in the upper plate. A flat subduction style is shown to have an important thermal impact resulting in a much colder plate interface and may succeed in explaining the apparent increase in coupling.