1. A method of aligning sentences in a first corpus with sentences in a second corpus, the method comprising: applying a length-based alignment model to the first corpus and the second corpus to align sentence boundaries for at least one sentence in the first corpus with sentence boundaries for a sentence in the second corpus to produce at least one aligned sentence pair; using the aligned sentence pairs to train a translation model; and applying the translation model to the first corpus and the second corpus to align sentence boundaries for at least one sentence in the first corpus with sentence boundaries for a sentence in the second corpus.