This paper reports on a longitudinal study designed to assess the progress made by UK foreign language undergraduate students during the residence abroad (RA) component of their degree. The article first of all places the study within the international research context, and then describes the data collation procedures and methodology employed. It reports findings concerning proficiency gains and the predictive validity of factors such as gender, IQ, length of stay, prior levels of achievement and previous methodological exposure. The findings confirm significant linguistic gains in general for RA. They also appear to show that individuals vary greatly in their rates of progress during RA on holistic measures of proficiency but that previous methodological exposure is a key factor in determining gains on discrete measures. There is also evidence that longer stays do not necessarily lead to greater proportionate proficiency gains. Findings concerning progress, prediction of progress and individual performance variation are compared and contrasted with those of American and other British studies. (Contains 13 tables, 2 figures, and 6 notes.)