WordNet::Similarity is a freely available software package that measures the semantic similarity and relatedness between pairs of concepts (or synsets) using the lexical database WordNet. It provides six measures of similarity and three measures of relatedness, all implemented as Perl modules. The similarity measures, such as res, lin, and jen, are based on the information content of the least common subsumer (LCS) of the concepts, while the relatedness measures, such as hso, lesk, and vector, are more flexible and can be applied across parts of speech. The package supports both command-line and programming interfaces, allowing users to interactively measure similarity and incorporate these measures into Perl programs. WordNet::Similarity has been used in various research domains, including word sense disambiguation, cross-document structural relationship identification, and multiword expression evaluation. The software is available under the GNU Public License from CPAN and SourceForge.WordNet::Similarity is a freely available software package that measures the semantic similarity and relatedness between pairs of concepts (or synsets) using the lexical database WordNet. It provides six measures of similarity and three measures of relatedness, all implemented as Perl modules. The similarity measures, such as res, lin, and jen, are based on the information content of the least common subsumer (LCS) of the concepts, while the relatedness measures, such as hso, lesk, and vector, are more flexible and can be applied across parts of speech. The package supports both command-line and programming interfaces, allowing users to interactively measure similarity and incorporate these measures into Perl programs. WordNet::Similarity has been used in various research domains, including word sense disambiguation, cross-document structural relationship identification, and multiword expression evaluation. The software is available under the GNU Public License from CPAN and SourceForge.