Year 400 (CD) was a leap year starting on Sunday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Stilicho and Aurelianus (or, less frequently, year 1153 Ab urbe condita). The denomination 400 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Below is a list of the 28 Major League Baseball players who have reached the .400 batting average milestone in a single season.