Void for Vagueness
A defendant in the United States may be able to challenge a statute on grounds that it violates the fundamental due process clause of the 5th and 14th Amendment of the United States Constitution because it is overly vague. The void for vagueness doctrine has its roots in the notion that everyone should have fair notice of what constitutes a crime. The requirement that statutes be narrowly tailored statutes is one of the cornerstones of the legality principle. Not every statute which appears vague will be void for vagueness. Every statute involves some degree of vagueness and rightly so because criminal codes must be narrow enough to provide notice but broad enough to capture unanticipated variations in criminal activity.
In contrast to vagueness, sometimes a statute will be ambiguous. A statute is ambiguous if it can be interpreted in two ways. If a statute is ambiguous, it should be construed in favor of the defendant.
The doctrine was explained in Jordan v. De George:
The essential purpose of the "void for vagueness" doctrine is to warn individuals of the criminal consequences of their conduct. Williams v. United States, 341 U.S. 97, decided April 23, 1951; Screws v. United States, 325 U.S. 91, 103-104 (1945). This Court has repeatedly stated that criminal statutes which fail to give due notice that an act has been made criminal before it is done are unconstitutional deprivations of due process of law. Lanzetta v. New Jersey, 306 U.S. 451 (1939); United States v. Cohen Grocery Co., 255 U.S. 81 (1921).
The test for whether a given statue is vague is objective in nature and asks whether the provision "fails to give a person of ordinary intelligence fair notice that his contemplated conduct is forbidden by the statute." 
"the terms of a penal statute must be sufficiently explicit to inform those who are subject to it what conduct on their part will render them liable to its penalties and a statute which either forbids or requires the doing of an act in terms so vague that men of common intelligence must necessarily guess at its meaning and differ as to its application violates the first essential of due process of law.
The rationale behind the void for vagueness doctrine rests on three interrelated principles:
First, citizens are entitled to notice of what is legal and what is illegal so that they can conform their conduct accordingly.
Second, statutes which are vague invest too much power in the prosecution, resulting in arbitrary and erratic arrests and convictions. For instance, in Papachristou v. City of Jacksonville the U.S. Supreme Court struck down a statute the criminalized vagrancy for those who were "loafing" or "wandering and strolling."  A vague law "impermissibly delegates basic policy matters to policemen, judges, and juries for resolution on an ad hoc and subjective basis, with the attendant dangers of arbitrary and discriminatory application."
Third, statutes which are void for vagueness provide judges with too much discretion in the application of the law.
When the defense of void for vagueness is combined with an affirmative First Amendment claim, heightened scrutiny may apply.
- Jordan v. De George, 341 U.S. 223 (1951)
- United States v. Harriss, 347 U.S. 612, 617
- Connally v. General Const. Co,269 U. S. 385 (1926)
- Thornhill v. Alabama, 310 U.S. 88 ; Herndon v. Lowry, 301 U.S. 242
- Papachristou v. City of Jacksonville, 405 U.S. 156 (1972). See also Thornhill v. Alabama, 310 U.S. 88 ; Herndon v. Lowry, 301 U.S. 242
- Grayned v. City of Rockford, 408 U.S. 104, 108-09 (1972)
- Joseph Burstyn, Inc. v. Wilson, 343 U.S. 495(1952)