In legal documents, the verb shall is used to indicate obligation, to express a promise or to make a declaration to which the parties involved are legally bound. This use differs from that in everyday speech, where it is most often used to make offers (Shall I open the window?) or to refer to the future (I shall miss you), although this latter use is less frequent in modern English.
In legal texts, shall usually expresses the meaning of “must” (obligation):
Every notice of the meeting of the shareholders shall state the place, date and hour.
Or “will” (in the sense of a promise):
The board of directors shall have the power to enact bylaws.
Shall can also be used in legal texts to refer to a future action or state:
...until two years shall have expired since such action by vote of such shareholders.
In everyday speech, this future meaning is commonly expressed using only the present perfect (... until two years have expired...).
Another verb commonly found in legal documents is may, which generally expresses permission, in the sense of “can” (this use is less common in everyday English):
...any bylaw or amendment thereto as adopted by the Board of Directors may be altered, amended or repealed by a vote of the shareholders.
In everyday English, may is sometimes used as a substitute for might, indicating probability (He may want to see the document).
Amy Krois-Linder, International Legal English, Professional English, Cambridge.