The 21st (twenty-first) century is the current century in the Anno Domini era or Common Era, under the Gregorian calendar. It began on 1 January 2001 (MMI) and will end on 31 December 2100 (MMC). There is a lack of general agreement over how to pronounce specific years of the 21st century in English. Generally, the early years of the 21st century were pronounced as in "two-thousand (and) five", with a change taking place around 2010, when pronunciations often shifted between the early-years form of "two-thousand and ten" and the traditionally more concise form of "twenty-ten".

Source: Wikipedia