Common Era (also Current Era
or Christian Era),
abbreviated as CE, is an alternative naming of the traditional calendar era, Anno Domini (abbreviated AD).
BCE is the abbreviation for Before the Common/Current/Christian Era (an alternative to Before Christ, abbreviated BC).
The CE/BCE designation uses the year-numbering system introduced by the 6th-century Christian monk Dionysius Exiguus, who started the Anno Domini designation, intending the beginning of the life of Jesus to be the reference date.
Neither notation includes a year zero,
and the two notations (CE/BCE and AD/BC) are numerically equivalent; thus " CE" corresponds to "AD " and "399 BCE" corresponds to "399 BC".

The expression "Common Era" can be found as early as 1708 in English, and traced back to Latin usage among European Christians to 1615, as vulgaris aerae, and to 1635 in English as Vulgar Era. At those times, the expressions were all used interchangeably with "Christian Era", and "vulgar" meant "not regal" rather than "crudely indecent". Use of the CE abbreviation was introduced by Jewish academics in the mid-19th century. Since the later 20th century, use of CE and BCE has been popularized in academic and scientific publications, and more generally by publishers emphasizing secularism or sensitivity to non-Christians.

The Gregorian calendar, and the year-numbering system associated with it, is the calendar system with most widespread use 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 CE/BCE notation has been adopted by numerous authors and publishers wishing to be
neutral or sensitive to non-Christians
because it does not explicitly make use of religious titles for Jesus, such as "Christ" and Domin- ("Lord"), which are used in the BC/AD notation, nor does it give implicit expression to the Christian creed that Jesus was the Christ.
Among the reasons given by those who oppose the use of Common Era notation is that it is selective as other aspects of the Western calendar have origins in various belief systems (e.g., January is named for Janus),
and claims that its propagation is the result of secularization, anti-supernaturalism, religious pluralism, and political correctness.