This study is an investigation of the development of vocabulary knowledge during study abroad (SA), intensive domestic immersion (IM) and academic-year formal classroom (AY) learning. Its focus was the growth of vocabulary knowledge in Japanese--a language where little SA research has been conducted to date. Unlike most studies addressing vocabulary development, it was centered strictly on vocabulary acquisition. Following the example of one of the most insightful comparative studies of vocabulary learning abroad and at home to date (Laufer & Paribakht, 1998), it included multiple measures of vocabulary knowledge to assess possible subtle differences in vocabulary acquisition between the SA, IM and AY settings. The first research question to be addressed in this study was, "Are there differences in terms of vocabulary development between learners in SA, IM and AY settings?" The second question, focusing on the nature of interactions and efforts to use the second language was, "Is language contact correlated with vocabulary acquisition in the SA, IM and AY settings?" Results showed differences between contexts in terms of vocabulary acquisition. Furthermore, significant correlations were found between language contact and vocabulary acquisition in the SA, IM and AY settings. (Contains 6 tables and 8 notes.)