1. An alignment method comprising: for a source sentence in a source language, identifying whether the sentence includes at least one candidate term comprising a contiguous subsequence of words of the source sentence; aligning a target sentence in a target language with the source sentence, comprising: developing a probabilistic model which models conditional probability distributions for alignments between words of the source sentence and words of the target sentence; and generating an optimal alignment based on the probabilistic model, including, where the source sentence includes the at least one candidate term, enforcing a contiguity constraint which requires that all the words of the target sentence which are aligned with an identified candidate term form a contiguous subsequence of the target sentence.