Shall and will are two of the English modal verbs. They have various uses, including the expression of propositions about the future, in what is usually referred to as the future tense of English.

Historically, prescriptive grammar stated that, when expressing pure futurity (without any additional meaning such as desire or command), shall was to be used when the subject was in the first person, and will in other cases (e.g., "On Sunday, we shall go to church, and the preacher will read the Bible.") This rule is no longer commonly adhered to by any group of English speakers, and will has essentially replaced shall in nearly all contexts.

Shall is, however, still widely used in bureaucratic documents, especially documents written by lawyers. Owing to heavy misuse, its meaning can be ambiguous and the United States government's Plain Language group advises writers not to use the word at all. Other legal drafting experts, including Plain Language advocates, argue that while shall can be ambiguous in statutes (which most of the cited litigation on the word's interpretation involves), court rules, and consumer contracts, that reasoning does not apply to the language of business contracts. These experts recommend using shall but only to impose an obligation on a contractual party that is the subject of the sentence, i.e., to convey the meaning "hereby has a duty to."