Rights are difficult to define. The Bill Of Rights of the U.S. Constitution states certain basic rights, but ambiguity shrouds the meaning of almost every important phrase. In practice, rights are what courts, legislators, presidents, and governors say they are.

The meaning of civil rights has changed greatly over the years. The original concept was rooted in 18th-century politics and philosophy. The decay of absolute monarchy led to efforts to check and limit royal power. In England the political philosopher John Locke gave shape to the new concept of individual natural rights against the state. Locke also believed that natural rights should be guaranteed against incursions by other persons as well as by the state.

In France, at the beginning of the revolution of 1789, the new Constituent Assembly issued its Declaration of the Rights of Man and of the Citizen. "Men are born and remain free and equal in rights", including "liberty, property, security, and resistance to oppression."
Much of the Declaration was derived from the writings of Diderot, Lafayette, Mirabeau, Jean Jacques Rousseau and Voltaire.

In America, Thomas Jefferson expanded the English and American views of civil rights. He emphasized the primacy of human happiness, by which he meant the opportunity of autonomous individuals to develop themselves to the fullest. He also advanced the concept of religious freedom and church-state separation as a key element of civil rights.

The end of slavery marked a new chapter in the development of civil rights in the United States. After the Civil War a number of constitutional amendments were proposed. Three were designed primarily to protect the newly freed blacks and, less directly, other victims of discrimination. The 13th Amendment abolished slavery and involuntary servitude (including peonage). The 14th Amendment extended American citizenship to all those persons born or naturalized in the United States. It contained far-reaching provisions forbidding any state to "deprive any person of life, liberty, or property, without due process of law" or to deny any person "equal protection of the laws." The 15th Amendment extended the right of suffrage to blacks. The phrase "equal protection of the laws" became crucial in the 20th-century struggle against discrimination. Although the Supreme Court was slow to address the concept, it stands today as the major constitutional means for combating sex and race discrimination in America.

Throughout recent history, people have organized to struggle for rights to which they felt entitled either by law or by a sense of justice. In the United States, black militancy spread in the 1950s and '60s through the activities of the Congress of Racial Equality, the Southern Christian Leadership Conference headed by Martin Luther King, Jr., and the Student Nonviolent Coordinating Committee (S.N.C.C.). These groups achieved major successes in arousing national opinion against segregation in the South and in stimulating the civil rights legislation of the 1960s. They failed, however, to eliminate some of the deep-rooted segregation patterns in urban areas of the country.

The successes of black militants encouraged women activists. While the struggle for suffrage had achieved voting rights for U.S. women under the 19th amendment in 1920, women now sought equal treatment in other social relationships such as employment and property rights.

A similar movement gained momentum among U.S. homosexuals that aimed at winning legal safeguards against discrimination in employment, housing, and public accommodations.

Civil rights have been given broad recognition in many countries, particularly in Great Britain, Western Europe, Scandinavia, Australia, New Zealand, and Japan. In many other countries, however, civil rights are empty phrases in constitutions and other documents, and they are not recognized in practice.

Nevertheless, even such lip service is a testimony to the growing consciousness of rights everywhere. The United Nations General Assembly gave expression to this consciousness in its Universal Declaration of Human Rights in 1948, and in subsequent covenants on civil and political rights and on economic, social, and cultural rights.