Established the principle of clear and present danger: the government may only restrict free speech if it presents a "clear and present danger" to the government or the nation. Does not apply in all situations (see Brandenburg v. Ohio).
Established the exclusionary principle, allowing evidence obtained from a violation of due process to be removed from criminal proceedings in some instances.
Lower courts must provide legal counsel for indigent defendants in all felony proceedings.
Extended the 9th Amendment right to (marital) privacy to include the right to use contraceptives and the right to refrain from telling a marital partner about using contraceptives.
Ruled that those charged of a crime must be informed of their privilege against self-incrimination and their right to legal counsel.
Declared student free speech to be protected unless it disrupts education.
Established the principle of "grave and irreparable damage": for the government to restrict someone's freedom of the press by prior restraint (censoring something before it is published), they must first prove that publishing the document, article, etc. would result in "grave and irreparable damage" to the nation or the government.
Expanded the 9th Amendment right to privacy to include that of women to get an abortion and that of doctors to conduct abortion services. Women have the right to an abortion until viability, and doctors have the right to be free from legal or professional repercussions from assisting in an abortion.
Extended the 1st Amendment freedom of speech to include desecration of the American flag, under the reasoning that the deliberate destruction of a nation's flag is inherently a form of expression. Invalidated prohibitions on the desecration of the American flag.
Expanded the 9th Amendment right to (marital) privacy to include not informing a spouse about having an abortion. The States cannot require that women have spousal awareness before getting an abortion.
Ruled that the US Attorney-General cannot prohibit physician-assisted suicide.
Extended the 2nd Amendment to non-military purposes in federal enclaves.
Incorporated the 2nd Amendment against the States, and ruled that it protects firearms kept for non-military purposes.