The author argues that the thought of American polymath Charles Sanders Peirce (1839–1914) offers a coherent, adequate, and versatile framework for understanding the eucharistic species as “signs.” Specifically, the historical analyses in the first and second parts of the article provide a conceptual grammar for showing the usefulness of Peirce’s sign theory to interpret the understanding of the Eucharist as expressed in Sacrosanctum concilium (1963). The article concludes by suggesting how these clarifications might help promote cross-disciplinary study of the liturgy.