NLTK

Generations of NLP practitioners learned the field through NLTK, the Natural Language Toolkit, a suite of open source Python modules, datasets, and tutorials for working with human language data. It bundles interfaces to dozens of corpora and lexical resources, including WordNet, alongside libraries for tokenization, stemming, part-of-speech tagging, parsing, and text classification. The toolkit pairs with the freely available book Natural Language Processing with Python, which made it a standard choice in university courses, and current releases support Python 3.10 through 3.14. Source code is Apache 2.0 licensed, with documentation under a Creative Commons license and individual corpora under their own redistributable terms. Production systems often reach for faster libraries, but NLTK remains a reference toolkit for teaching, prototyping, and research where breadth of classical algorithms and annotated corpora matters more than raw speed.