This discipline studies, from a computational perspective, all levels of language from the production of speech to the meanings of texts and dialogues. And over the past 40 years, NLP has produced an impressive computational infrastructure of resources, techniques, and tools for analyzing sound structure (phonology), word structure (morphology), grammatical structure (syntax) and meaning structure (semantics). As well as being important for language-based applications, this computational infrastructure makes it possible to investigate the structure of human language and communication at a deeper scientific level than was ever previously possible.