This report is a compilation of five research papers in second language acquisition and immigrant adaptability that are part of studies conducted in Sweden over the last twenty years. (1) "Language teaching and psycho-physics" discusses basic measurement problems in the assessment of second language proficiency, where testing of writing and reading skills has overshadowed listening comprehension and pronunciation skills in importance. (2) "Measuring foreign language achievement in the ages 7-10 years" deals with the optimum age problem in second language learning when the setting is modern language learning in a school situation, and tests the possibility of the formation of learning sets. (3) "Age and length of residence as variables related to the adjustment of migrant children" complements the above discussion on optimum age problems, with the setting as language learning in a foreign cultural environment. (4) "Adjustment among immigrant peoples in Sweden" studies the relation between language learning and socio-emotional adjustment. (5) "Social and individual frame factors in second language acquisition: Comparative aspects" considers a number of variables in the two language learning situations described above. It is concluded that different levels of measurement of language functions such as the physical, psychological, neuro-physiological, neurological, educational, and linguistic levels, should be regarded as complementary, not exchangeable. (Author/MHP)