Evidential constructions have two main semantic effects: They contribute information about an individual's source of evidence, and they potentially modify the force of a sentence. In this article, I review the at-issue status of the evidential information, the indexical and anaphoric properties of evidentials, their force-modifying effect, and the connection throughout to epistemic modality. In some languages, evidentials occur as part of the grammatical morphology, but evidential information can be expressed through a variety of constructions across languages. As such, the study of evidentiality highlights the important role of cross-linguistic semantics and the collaboration between language typology and linguistic semantics. Expected final online publication date for the Annual Review of Linguistics, Volume 7 is January 14, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.