Typically, calendar eras represent long time periods. In the Gregorian calendar, for example, the current era spans (as of this year) 2,018 years. In the Japanese calendar, however, a new era begins with the reign of a new emperor. On April 30, 2019, Emperor Akihito is expected to abdicate, which will bring to an end the Heisei era. On the following day, when his successor becomes emperor, a new era in the Japanese calendar will begin. It is the first transition from one era to another in the history of .NET, and the first change of eras in the Japanese calendar since Emperor Akihito’s accession in January 1989. In this blog post, I’ll discuss how eras work in general in .NET, how you can determine whether your application is affected by the era change, and what you as a developer have to do to make sure your application handles the upcoming Japanese era changes successfully.