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).[1]

Marking the beginning of the 21st century was the rise of a global economy and Third World consumerism, deepening global concern over terrorism after 11 September 2001, terrorist attacks and increased private enterprise.[2][3][4] The NATO interventions in Afghanistan and Iraq of the early 2000s and overthrowing several regimes during the Arab Spring of the early 2010s led to mixed outcomes in the Arab world, resulting in several civil wars and political instability.[5] The United States has remained the global superpower, while China is now considered an emerging superpower.

In 2017, 49.3% of the world's population lived in "some form of democracy", though only 4.5% lived in "full democracies".[6] The United Nations estimates that by 2050 two thirds of the world's population will be urbanized; an inverse of a century ago when less than one-third lived in cities.

The European Union was greatly expanded in the 21st century, adding 13 member states, but the United Kingdom withdrew. Most European Union member states introduced a common currency, the Euro. The North Atlantic Treaty Organization (NATO) was also greatly expanded in the 21st century, adding 11 member states.

Effects of global warming and rising sea levels exacerbated the ecological crises, with eight islands disappearing between 2007 and 2014.[7][8][9]

In early 2020, the COVID-19 pandemic began to rapidly spread worldwide, killing over 6 million people around the globe and causing severe global economic disruption, including the largest global recession since the Great Depression.

With the proliferation of mobile devices, more than half of the world's population obtained access to the Internet by 2018.[10] After the success of the Human Genome Project, DNA sequencing services became available and affordable.[11][12]