The Manually Annotated Sub-Corpus (MASC) consists of approximately 500,000 words of contemporary American English written and spoken data drawn from the OPEN AMERICAN NATIONAL CORPUS (OANC).

All of MASC includes manually validated annotations for sentence boundaries, token, lemma and POS; noun and verb chunks; and named entities (person, location, organization, date). Additional manually produced or validated annotations have been produced by the MASC project for portions of the sub-corpus, including full-text annotation for FrameNet frame elements, WordNet sense tags, and Penn Treebank syntactic annotation. Annotations of all or portions of the sub-corpus for a wide variety of other linguistic phenomena have been contributed by other projects.

Unlike most freely available corpora including a wide variety of linguistic annotations, MASC contains texts from a broad range of genres.

MASC is an OPEN LANGUAGE DATA resource that can be downloaded by anyone for any purpose. At the same time, it is a resource that will be enhanced by the community, through its contributions of annotations and derived data.