The first public presentation of the ideas leading up to the Interlanguage (IL) Hypothesis occurred a decade ago at the Second International Congress of Applied Linguistics (Selinker 1969; presented in greater detail in Selinker 1972). At that time, it was stated that, in attempting to understand the phenomenon of second-language learning, the field was at a stage where there existed an “inability to unambiguously identify the phenomena we wish to study” (Selinker 1969:35). That first presentation of the IL notion focused on the “psychologically relevant data of second-language learning,” trying to describe what it was that should be studied; the paper attempted to provide some theoretical constructs which would help identify and explain that data.