This study applies structuralist insights into the mechanisms of contact‐induced language change to an examination of the selectivity of L1 influence on L2 acquisition. The principle of selectivity refers to formal properties that make L2 structures immune or receptive to L1 influence as well as L2 developmental stages that activate L1 transfer along a time axis. Basic to the approach set forth is the structuralist assumption that a language will accept only those external influences that correspond to its own structural tendencies and systemic biases. It is proposed that areas of an L2 potentially susceptible to L1 influence can be identified through an examination of that L2's learner‐language. This entity refers to developmental aspects of the acquisition of that L2 both as a first and as a second language.The paper examines in some detail the formal parameters that govern the selectivity of L1 transfer. The proposed approach is capable of accounting in a principled way for conflicting findings reported in L2 research on the occurrence and non‐occurrence of structural tra