Nobility is a social class which possesses more acknowledged privileges or eminence than members of most other classes in a society, membership therein typically being hereditary. The privileges associated with nobility may constitute substantial advantages over or relative to non-nobles, or may be largely honorary (e.g. precedence), and vary from country to country and era to era. Historically membership in the nobility and the prerogatives thereof have been regulated or acknowledged by the government, thereby distinguishing it from other sectors of a nation's upper class. Nonetheless, nobility per se has rarely constituted a closed caste; acquisition of sufficient power, wealth, military prowess or royal favour has, occasionally or often, enabled commoners to ascend into the nobility.
There is often a variety of ranks within the noble class. Legal recognition of nobility has been more common in monarchies, but nobility also existed in such republics as the Dutch Republic (1581–1795), Republic of Genoa (1005–1815) and Republic of Venice (697–1797), and remains part of the legal social structure of some non-hereditary regimes, e.g. San Marino and Vatican City in Europe. Hereditary titles often distinguish nobles from non-nobles, although in many nations most of the nobility have been un-titled, and a hereditary title need not indicate nobility (e.g., baronet).