This chapter presents some of the basic language engineering pre-processing steps (tokenization, part-of-speech tagging, lemmatization, and sentence and word alignment). Tagging is among the most important processing steps and its accuracy significantly influences any further processing. Therefore, tagset design, validation and correction of training data and the various techniques for improving the tagging quality are discussed in detail. Since sentence and word alignment are prerequisite operations for exploiting parallel corpora for a multitude of purposes such as machine translation, bilingual lexicography, import annotation etc., these issues are also explored in detail.