Machine Translation (MT) is the translation of text by a computer. There are two types of machine translation systems: rule-based and statistical systems. Rule-based systems use a combination of dictionaries and (grammar) rules. Statistical systems do not work with 'rules', but derive all information necessary to translate from large collections of texts. To produce high-quality translations, humans still need to intervene in the process either by making the input more suitable for MT (pre-editing) or changing the output (post-editing).