Six papers on interlanguage are presented. The first, "Language Transfer," experimentally tests Robert Lado's contrastive analysis principles on the transfer of language skills to second language acquisition. The second paper, called "Interlanguage," builds on this work in discussing the structured nature of interlanguage and autonomous material found in interlanguage that is in neither the native nor the target language. The third paper, "The Interlanguage Hypothesis Extended to Children," reports on data gathered in a Toronto French immersion program, showing that, at least in some settings, it is plausible to infer that young children do form interlanguages. The paper called "Systematicity/Variability and Stability/Instability in Interlanguage Systems" addresses a number of issues concerning variation in interlanguages, based on variable data from morphology, syntax, and semantics. The fifth paper, "Two Perspectives on Fossilization in Interlanguage Learning," looks at the "strong" and "weak" conceptions of fossilized language that argue for or against the inevitability of fossilization, and the potential for teaching communication under these conditions. The last paper, "Researching the Discourse Domains View of Interlanguage," summarizes recent work in this field, focusing, to some degree, on the application of discourse analysis to Southeast Asian languages and language instruction. A list of 142 references is included. (MSE)