We study in this chapter the problem of measuring the degree of comparability of bilingual corpora, with applications to bilingual lexicon extraction. We first develop a measure which can capture different comparability levels. This measure correlates very well with gold-standard comparability levels and is relatively robust to dictionary coverage. We then propose a well-founded algorithm to improve the quality, in terms or comparability scores, of exiting comparable corpora, prior to showing that the bilingual lexicons extracted from corpora enhanced in this way are of better quality. All the experiments in this chapter are performed on French-English comparable corpora.