Concord is agreement in gender, case, number or person between different words that share a reference. For example, if a sentence contains a proper noun "Paul" and somewhat later a pronoun "he," and they refer to the same person, we say that they agree in number (for both are singular) and gender (for both are masculine).

In Modern English, the rules of concord are relatively simple, and these rules also apply to Old English:

Concord differs in Old and Modern English mainly in that adjectives and demonstrative pronouns are marked for gender, case and number in Old English, and they therefore participate in the system of concord. We can therefore add these rules to the ones that are familiar to us from Modern English: Old English Aerobics contains two sessions on concord. The first concerns the agreement of demonstrative pronouns and strong adjectives with the nouns they modify, and the second concerns agreement between subject and verb.