In one respect, there really is no difference between an AD/BC and BCE/CE system when it comes to historical dates. The year 23 AD is exactly the same as the year 23 CE, and 4004 BC is also 4004 BCE. References to historical dates under either classification shouldn't create confusion in a researcher's mind. Major historical dates such as 1492 AD, 1776 AD or 1941 AD would still be rendered as 1492 CE, 1776 CE and 1941 CE.

The AD/BC method of identifying historical dates can be traced back to Catholic historians working in the early Middle Ages. Identifying historical dates until that point was often a complicated proposition, since different historians worked under different calendars. A Roman historian such as Josephus would have used the Roman AUD notation, in which Year Zero was the largely symbolic founding of Rome. Converting historical dates to the standard Gregorian calendar would not have been easy. Using the birth of Jesus Christ as a central point made more sense to the religious historians.

The term BC is short for "Before Christ". Historical dates before the birth of Christ become smaller as they approach the theoretical but non-existent Year Zero. Historical dates after the birth of Christ are classified as AD, short for the Latin phrase Anno Domini, or "in the year of our Lord". Contrary to popular belief, AD does not stand for "After Death". The BC/AD system for identifying historical dates has been in continuous use ever since the earliest part of the Middle Ages, at least.

Several centuries after the AD/BC identification of historical dates became popular, a new movement developed among scientists, historians and some religious leaders. The time following the birth of Christ was now referred to as the "Vulgar Era" in some circles. The meaning of the word vulgar actually meant 'common' at that time, not distasteful or obscene. Eventually many areas of the Western world adopted the less Christ-centered term "Common Era". Historical dates occurring before the year 1 CE would be considered BCE, short for "Before Common Era".

The relatively new BCE/CE reference for historical dates has had its share of supporters and critics. Critics view the new system as an attempt to remove the religious significance inherent in the BC/AD system. The BCE/CE method of assigning historical dates also fails to fix the BC/AD system's lack of a practical Year Zero. Modern scholars believe the actual birth of Christ would fall around 7 to 4 BC, which renders the actual year of 1 AD relatively meaningless historically.

Supporters of the BCE/CE method of identifying historical dates say the removal of Christian references works as a bridge between different religions and cultures. The BC/AD system appears to endorse Jesus Christ as the superior world religious figure, which could be viewed as disrespectful of other religions and belief structures. Although the birth of Christ is still used as a reference in the BCE/CE system, the Christian influence is not as apparent.

Some have argued that the religious significance of the BC/AD method has already been largely forgotten, so the need for change is not readily apparent. The use of BCE/CE is still quite limited, although some experts see it becoming the dominant means of identifying historical dates within a century or two.