Before common era

Common Era or Current Era (CE) is a year-numbering system (calendar era) for the Julian and Gregorian calendars that refers to the years since the start of this era, i.e., since AD 1. The preceding era is referred to as before the Common or Current Era (BCE). The Current Era notation system can be used as a secular alternative to the Dionysian era system, which distinguishes eras as AD (anno Domini, "[the] year of [the] Lord") and BC ("before Christ"). The two notation systems are numerically equivalent; thus "2017 CE" corresponds to "AD 2017" and "400 BCE" corresponds to "400 BC". The year-numbering system for the Gregorian calendar is the most widespread civil calendar system used in the world today. For decades, it has been the global standard, recognized by international institutions such as the United Nations and the Universal Postal Union.

The expression has been traced back to Latin usage to 1615, as vulgaris aerae, and to 1635 in English as "Vulgar Era". The term "Common Era" can be found in English as early as 1708, and became more widely used in the mid-19th century by Jewish academics. In the later 20th century, the use of CE and BCE was popularized in academic and scientific publications, and more generally by authors and publishers wishing to emphasize secularism or sensitivity to non-Christians, by not explicitly referencing Jesus as "Christ" and Dominus ("Lord"), shortened from anno Domini nostri Jesu Christi ("in the year of Our Lord Jesus Christ").

The year numbering system used with Common Era notation was devised by the Christian monk Dionysius Exiguus in the year 525 to replace the Era of Martyrs system, because he did not wish to continue the memory of a tyrant who persecuted Christians. He attempted to number years from an initial reference date ("epoch"), an event he referred to as the Incarnation of Jesus. Dionysius labeled the column of the table in which he introduced the new era as "Anni Domini Nostri Jesu Christi".

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