Incorporation is a legal doctrine applied by the U.S. judicial system which applies the liberties and protections of Bill of Rights in the jurisdiction of the state and local governments. This means the same limitations which apply to laws written and executed at the federal level must also be observed by lower level governments. For the first 150 years of constitutional interpretation, the Bill of Rights applied against only the federal government. Incorporation is only an interpretation of the U.S. Constitution and is not institutionalized, meaning incorporation is not written into the legal framework of the government rather it has been interpreted into the framework by justices on the U.S. Supreme Court. This means that rights could be unincorporated though this is unlikely due to the tradition of legal precedent.
Rights and privileges of the citizens are currently incorporated by means of the Fourteenth Amendment. The Due Process Clause read “substantively” allows justices to apply a more modern meaning to the Fourteenth Amendment that incorporates “fundamental rights necessary to our system of ordered liberty.” The first piece of the Bill of Rights to be incorporated was just compensation of the Fifth Amendment in 1897 in the case Chicago, Burlington & Quincy Railroad Co. v. City of Chicago. The writer of the majority opinion in that case was Justice John Marshall Harlan joined by 6 other justices. The last amendment to be incorporated was the Second Amendment in the 2010 case McDonald v. Chicago.
Another theory to incorporation is use of the Privileges and Immunities Clause also embedded in the text of the Fourteenth Amendment. This was used by lawyers during the Slaughterhouse Cases in the 1870s but without success because the Court choose to read this provision with the legislative intent as applying only to freed slaves. In his concurring opinion in the 2010 case McDonald v. Chicago, Justice Clarence Thomas argues that the Privilege and Immunities Clause should be revisited as the proper vehicle through which the Bill of Rights is incorporated.
Historically the doctrine has been interpreted as selective incorporation. Not every right in the Constitution applies to the state and local governments. The Supreme Court has evaluated arguments on a case-by-case basis to determine the necessity of incorporating the right in question. Justice Hugo Black was a leading proponent of total incorporation: the idea that the entire Bill of Rights should be incorporated en bloc through the Due Process Clause of the Fourteenth Amendment.