AD and BC are abbreviations used to label years in the Gregorian calendar, which is the global standard for measuring dates. AD stands for "Anno Domini," which is Latin for "in the year of the Lord," and it refers specifically to the birth of Jesus Christ. BC stands for "Before Christ," and it indicates the number of years before the birth of Jesus Christ. The year Christ was born is considered AD 1, and the year before that is labeled 1 BC.

In recent years, an alternative form of BC/AD has gained traction, which is BCE (Before the Common Era) and CE (Common Era) . BCE stands for "before the common (or current) era," while CE stands for "common (or current) era". These abbreviations have a shorter history than BC and AD, although they still date from at least the early 1700s. They have been in frequent use by Jewish academics for more than 100 years, but became more widespread in the later part of the 20th century, replacing BC/AD in a number of fields, notably science and academia.

Most style guides do not express a preference for one system, although BC/AD still prevails in most journalistic contexts. Conversely, academic and scientific texts tend to use BCE/CE. Since there are compelling arguments for each system and both are in regular use, we do not recommend one over the other. Given the choice, writers are free to apply their own preference or that of their audience, although they should use their chosen system consistently, meaning BC and CE should not be used together, or vice versa.