An Examiner may require that the claims in a patent application be restricted to a single "independent and distinct" invention. This type of Office action is called a "requirement for restriction." Any response to such an Office action must include an election of the single invention to which the claims (and, hence, examination) will be restricted. The election must be filed no later than one month after the mailing date of the requirement for restriction, if the requirement is made without an action by the Examiner on the merits of the claims. The response period may be extended by up to 5 months by payment of extension fees. In no event can the response period exceed 6 months.