PyStemmer provides access to efficient algorithms for calculating a "stemmed" form of a word. This is a form with most of the common morphological endings removed; hopefully representing a common linguistic base form. This is most useful in building search engines and information retrieval software; for example, a search with stemming enabled should be able to find a document containing "cycling" given the query "cycles".

PyStemmer provides algorithms for several (mainly European) languages, by wrapping the libstemmer library from the Snowball project in a Python 3 module.

It also provides access to the classic Porter stemming algorithm for English: although this has been superseded by an improved algorithm, the original algorithm may be of interest to information retrieval researchers wishing to reproduce results of earlier experiments.