Abstract: A power train infinitely variable from substantially 1:1 ratio to a very high ratio, employing a pair of planetary gear assemblies, each including a sun gear, a ring gear and a planetary carrier having at least one planetary gear operatively connecting the associated ring and sun gears, the planetary gear assemblies having different gear ratios, both planetary assemblies having their sun gears rotatable by a driving member, a driven member operatively connected to the planetary carrier of the assembly of higher ratio, the ring gears being constructed for rotation as a unit, and the planetary carrier of the assembly of lower ratio being variably connectible with the driving member, whereby the overall ratio between driving and driven members is variable in dependence upon the relative speed of the driving member and the planetary carrier of the lower ratio assembly.