The 21st century is the current century of the Anno Domini era or the Common Era, in accordance with the Gregorian calendar.It began on January 1, 2001, and will end on December 31, 2100. It is the first century of the 3rd millennium.It is distinct from the century known as the 2000s, which began on January 1, 2000 and will end December 31, 2099.he 21st century is the current century of the Anno Domini era or the Common Era, in accordance with the Gregorian calendar.