We give a complete topological classification of properly embedded minimal surfaces in Euclidian three-space. 1. Introduction In 1980, Meeks and Yau [15] proved that properly embedded minimal surfaces of finite topology in R3 are unknotted in the sense that any two such homeomorphic surfaces are properly ambiently isotopic. Later Frohman [6] proved that any two triply periodic minimal surfaces in R3 are properly ambiently isotopic.