The standards that courts apply to determine whether a State has unconstitutionally excluded a private speaker from use of a public forum depend on the nature of the forum. See Perry Ed. Assn. v. Perry Local Educators' Assn., 460 U. S. 37, 44 (1983). If the forum is a traditional or open public forum, the State's restrictions on speech are subject to stricter scrutiny than are restrictions in a limited public forum. Id., at 45-46. When the State establishes a limited public forum, the State is not required to and does not allow persons to engage in every type of speech. The State may be justified 'in reserving [its forum] for certain groups or for the discussion of certain topics.' Rosenberger v. Rector and Visitors of Univ. of Va., 515 U. S. 819, 829 (1995). The State's power to restrict speech, however, is not without limits. The restriction must not discriminate against speech on the basis of viewpoint, and the restriction must be 'reasonable in light of the purpose served by the forum,' Cornelius v. NAACP Legal Defense & Ed. Fund, Inc., 473 U. S. 788, 806 (1985).